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Another round of careful revisions.
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Guido van Rossum
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Doc/ref.tex
381
Doc/ref.tex
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@ -49,7 +49,10 @@ informal introduction to the language, see the {\em Python Tutorial}.
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\pagebreak
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{
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\parskip = 0mm
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\tableofcontents
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}
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\pagebreak
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@ -84,6 +87,11 @@ standard modules. These are not documented here, but in the separate
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mentioned when they interact in a significant way with the language
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definition.
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\section{Warning}
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This version of the manual is incomplete. Sections that still need to
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be written or need considerable work are marked with ``XXX''.
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\section{Notation}
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The descriptions of lexical analysis and syntax use a modified BNF
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@ -150,7 +158,17 @@ Two or more physical lines may be joined into logical lines using
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backslash characters (\verb/\/), as follows: when a physical line ends
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in a backslash that is not part of a string literal or comment, it is
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joined with the following forming a single logical line, deleting the
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backslash and the following end-of-line character.
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backslash and the following end-of-line character. For example:
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%
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\begin{verbatim}
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samplingrates = (48000, AL.RATE_48000), \
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(44100, AL.RATE_44100), \
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(32000, AL.RATE_32000), \
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(22050, AL.RATE_22050), \
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(16000, AL.RATE_16000), \
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(11025, AL.RATE_11025), \
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( 8000, AL.RATE_8000)
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\end{verbatim}
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\subsection{Blank lines}
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@ -192,6 +210,9 @@ of Python code:
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\begin{verbatim}
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def perm(l):
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# Compute the list of all permutations of l
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if len(l) <= 1:
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return [l]
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r = []
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@ -239,10 +260,9 @@ uppercase: "A"..."Z"
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digit: "0"..."9"
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\end{verbatim}
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Identifiers are unlimited in length. Case is significant. Keywords
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are not identifiers.
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Identifiers are unlimited in length. Case is significant.
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\section{Keywords}
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\subsection{Keywords}
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The following identifiers are used as reserved words, or {\em
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keywords} of the language, and cannot be used as ordinary
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@ -322,8 +342,8 @@ but you may end up quadrupling backslashes that must appear literally.)
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\subsection{Numeric literals}
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There are three types of numeric literals: integers, long integers,
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and floating point numbers.
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There are three types of numeric literals: plain integers, long
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integers, and floating point numbers.
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Integers and long integers are described by the following regular expressions:
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@ -339,25 +359,43 @@ octdigit: "0"..."7"
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hexdigit: digit|"a"..."f"|"A"..."F"
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\end{verbatim}
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Although both lower case `l'and upper case `L' are allowed as suffix
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for long integers, it is strongly recommended to always use `L', since
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the letter `l' looks too much like the digit `1'.
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(Plain) integer decimal literals must be at most $2^{31} - 1$ (i.e., the
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largest positive integer, assuming 32-bit arithmetic); octal and
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hexadecimal literals may be as large as $2^{32} - 1$. There is no limit
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for long integer literals.
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Some examples of (plain and long) integer literals:
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\begin{verbatim}
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7 2147483647 0177 0x80000000
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3L 79228162514264337593543950336L 0377L 0100000000L
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\end{verbatim}
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Floating point numbers are described by the following regular expressions:
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\begin{verbatim}
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floatnumber: [intpart] fraction [exponent] | intpart ["."] exponent
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floatnumber: pointfloat | exponentfloat
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pointfloat: [intpart] fraction | intpart "."
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exponentfloat: (intpart | pointfloat) exponent
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intpart: digit+
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fraction: "." digit+
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exponent: ("e"|"E") ["+"|"-"] digit+
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\end{verbatim}
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Some examples of numeric literals:
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The range of floating point literals is implementation-dependent.
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Some examples of floating point literals:
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\begin{verbatim}
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1 1234567890 0177777 0x80000
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3.14 10. .001 1e100 3.14e-10
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\end{verbatim}
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Note that the definitions for literals do not include a sign; a phrase
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like \verb\-1\ is actually an expression composed of the operator
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Note that numeric literals do not include a sign; a phrase like
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\verb\-1\ is actually an expression composed of the operator
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\verb\-\ and the literal \verb\1\.
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\section{Operators}
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@ -395,12 +433,6 @@ They may be used by future versions of the language though!
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\chapter{Execution model}
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(XXX This chapter should explain the general model of the execution of
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Python code and the evaluation of expressions. It should introduce
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objects, values, code blocks, scopes, name spaces, name binding,
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types, sequences, numbers, mappings, exceptions, and other technical
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terms needed to make the following chapters concise and exact.)
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\section{Objects, values and types}
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I won't try to define rigorously here what an object is, but I'll give
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@ -409,37 +441,41 @@ some properties of objects that are important to know about.
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Every object has an identity, a type and a value. An object's {\em
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identity} never changes once it has been created; think of it as the
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object's (permanent) address. An object's {\em type} determines the
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operations that an object supports (e.g., can its length be taken?)
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and also defines the ``meaning'' of the object's value; it also never
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changes. The {\em value} of some objects can change; whether an
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object's value can change is a property of its type.
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operations that an object supports (e.g., does it have a length?) and
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also defines the ``meaning'' of the object's value. The type also
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never changes. The {\em value} of some objects can change; whether
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this is possible is a property of its type.
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Objects are never explicitly destroyed; however, when they become
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unreachable they may be garbage-collected. An implementation,
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however, is allowed to delay garbage collection or omit it altogether
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-- it is a matter of implementation quality how garbage collection is
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implemented. (Implementation note: the current implementation uses a
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unreachable they may be garbage-collected. An implementation is
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allowed to delay garbage collection or omit it altogether -- it is a
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matter of implementation quality how garbage collection is
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implemented, as long as no objects are collected that are still
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reachable. (Implementation note: the current implementation uses a
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reference-counting scheme which collects most objects as soon as they
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become onreachable, but does not detect garbage containing circular
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become onreachable, but never collects garbage containing circular
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references.)
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Note that the use of the implementation's tracing or debugging
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facilities may keep objects alive that would normally be collectable.
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(Some objects contain references to ``external'' resources such as
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open files. It is understood that these resources are freed when the
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object is garbage-collected, but since garbage collection is not
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guaranteed such objects also provide an explicit way to release the
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external resource (e.g., a \verb\close\ method) and programs are
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guaranteed, such objects also provide an explicit way to release the
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external resource (e.g., a \verb\close\ method). Programs are strongly
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recommended to use this.)
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Some objects contain references to other objects. These references
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are part of the object's value; in most cases, when such a
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``container'' object is compared to another (of the same type), the
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comparison takes the {\em values} of the referenced objects into
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account (not their identities).
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comparison applies to the {\em values} of the referenced objects (not
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their identities).
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Except for their identity, types affect almost any aspect of objects.
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Even object identities are affected in some sense: for immutable
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Types affect almost all aspects of objects.
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Even object identity is affected in some sense: for immutable
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types, operations that compute new values may actually return a
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reference to an existing object with the same type and value, while
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reference to any existing object with the same type and value, while
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for mutable objects this is not allowed. E.g., after
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\begin{verbatim}
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@ -450,9 +486,13 @@ a = 1; b = 1; c = []; d = []
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\verb\c\ and \verb\d\ are guaranteed to refer to two different, unique,
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newly created lists.
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\section{The standard type hierarchy}
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XXX None, sequences, numbers, mappings, ...
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\section{Execution frames, name spaces, and scopes}
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XXX
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XXX code blocks, scopes, name spaces, name binding, exceptions
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\chapter{Expressions and conditions}
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@ -461,17 +501,17 @@ not lexical analysis.
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This chapter explains the meaning of the elements of expressions and
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conditions. Conditions are a superset of expressions, and a condition
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may be used where an expression is required by enclosing it in
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parentheses. The only place where an unparenthesized condition is not
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allowed is on the right-hand side of the assignment operator, because
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this operator is the same token (\verb\=\) as used for compasisons.
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may be used wherever an expression is required by enclosing it in
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parentheses. The only places where expressions are used in the syntax
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instead of conditions is in expression statements and on the
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right-hand side of assignments; this catches some nasty bugs like
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accedentally writing \verb\x == 1\ instead of \verb\x = 1\.
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The comma plays a somewhat special role in Python's syntax. It is an
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The comma has several roles in Python's syntax. It is usually an
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operator with a lower precedence than all others, but occasionally
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serves other purposes as well (e.g., it has special semantics in print
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statements). When a comma is accepted by the syntax, one of the
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syntactic categories \verb\expression_list\ or \verb\condition_list\
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is always used.
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serves other purposes as well; e.g., it separates function arguments,
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is used in list and dictionary constructors, and has special semantics
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in \verb\print\ statements.
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When (one alternative of) a syntax rule has the form
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@ -495,71 +535,89 @@ the following conversions are applied:
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the other is converted to floating point;
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\item else, if either argument is a long integer,
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the other is converted to long integer;
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\item otherwise, both must be short integers and no conversion
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\item otherwise, both must be plain integers and no conversion
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is necessary.
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\end{itemize}
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(Note: ``short integers'' in Python are at least 32 bits in size;
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(Note: ``plain integers'' in Python are at least 32 bits in size;
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``long integers'' are arbitrary precision integers.)
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\section{Atoms}
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Atoms are the most basic elements of expressions.
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Forms enclosed in reverse quotes or various types of parentheses
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or braces are also categorized syntactically as atoms.
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Syntax rules for atoms:
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Atoms are the most basic elements of expressions. Forms enclosed in
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reverse quotes or in parentheses, brackets or braces are also
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categorized syntactically as atoms. The syntax for atoms is:
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\begin{verbatim}
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atom: identifier | literal | parenth_form | string_conversion
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literal: stringliteral | integer | longinteger | floatnumber
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parenth_form: enclosure | list_display | dict_display
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enclosure: "(" [condition_list] ")"
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list_display: "[" [condition_list] "]"
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dict_display: "{" [key_datum ("," key_datum)* [","] "}"
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key_datum: condition ":" condition
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string_conversion:"`" condition_list "`"
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atom: identifier | literal | enclosure
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enclosure: parenth_form | list_display | dict_display | string_conversion
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\end{verbatim}
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\subsection{Identifiers (Names)}
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An identifier occurring as an atom is a reference to a local, global
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or built-in name binding. If a name can be assigned to anywhere in a code
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block, it refers to a local name throughout that code block.
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or built-in name binding. If a name can be assigned to anywhere in a
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code block, and is not mentioned in a \verb\global\ statement in that
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code block, it refers to a local name throughout that code block.
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Otherwise, it refers to a global name if one exists, else to a
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built-in name.
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When the name is bound to an object, evaluation of the atom
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yields that object.
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When it is not bound, a {\tt NameError} exception
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is raised, with the identifier as string parameter.
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When the name is bound to an object, evaluation of the atom yields
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that object. When a name is not bound, an attempt to evaluate it
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raises a {\tt NameError} exception.
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\subsection{Literals}
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Python knows string and numeric literals:
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\begin{verbatim}
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literal: stringliteral | integer | longinteger | floatnumber
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\end{verbatim}
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Evaluation of a literal yields an object of the given type
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(string, integer, long integer, floating point number)
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with the given value.
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The value may be approximated in the case of floating point literals.
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All literals correspond to immutable data types, and hence the object's
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identity is less important than its value.
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Multiple evaluations of the same literal (either the same occurrence
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in the program text or a different occurrence) may
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obtain the same object or a different object with the same value.
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All literals correspond to immutable data types, and hence the
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object's identity is less important than its value. Multiple
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evaluations of literals with the same value (either the same
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occurrence in the program text or a different occurrence) may obtain
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the same object or a different object with the same value.
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(In the original implementation, all literals in the same code block
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with the same type and value yield the same object.)
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\subsection{Enclosures}
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\subsection{Parenthesized form}
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An empty enclosure yields an empty tuple object.
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A parenthesized form is an optional condition list enclosed in
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parentheses:
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An enclosed condition list yields whatever that condition list yields.
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\begin{verbatim}
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parenth_form: "(" [condition_list] ")"
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\end{verbatim}
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(Note that, except for empty tuples, tuples are not formed by
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enclosure in parentheses, but rather by use of the comma operator.)
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A parenthesized condition list yields whatever that condition list
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yields.
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An empty pair of parentheses yields an empty tuple object (since
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tuples are immutable, the rules for literals apply here).
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(Note that tuples are not formed by the parentheses, but rather by use
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of the comma operator. The exception is the empty tuple, for which
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parentheses {\em are} required -- allowing unparenthesized ``nothing''
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in expressions would causes ambiguities and allow common typos to
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pass uncaught.)
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\subsection{List displays}
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A list display is a possibly empty series of conditions enclosed in
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square brackets:
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\begin{verbatim}
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list_display: "[" [condition_list] "]"
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\end{verbatim}
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A list display yields a new list object.
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If it has no condition list, the list object has no items.
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@ -568,36 +626,54 @@ from left to right and inserted in the list object in that order.
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\subsection{Dictionary displays}
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A dictionary display is a possibly empty series of key/datum pairs
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enclosed in curly braces:
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\begin{verbatim}
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dict_display: "{" [key_datum_list] "}"
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key_datum_list: [key_datum ("," key_datum)* [","]
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key_datum: condition ":" condition
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\end{verbatim}
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A dictionary display yields a new dictionary object.
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The key/datum pairs are evaluated from left to right to
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define the entries of the dictionary:
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each key object is used as a key into the dictionary to store
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the corresponding datum pair.
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The key/datum pairs are evaluated from left to right to define the
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entries of the dictionary: each key object is used as a key into the
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dictionary to store the corresponding datum.
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Keys must be strings, otherwise a {\tt TypeError} exception is raised.
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Clashes between keys are not detected; the last datum (textually
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rightmost in the display) stored for a given key value prevails.
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Keys must be strings, otherwise a {\tt TypeError} exception is raised.%
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\footnote{
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This restriction may be lifted in a future version of the language.
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}
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Clashes between duplicate keys are not detected; the last datum
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(textually rightmost in the display) stored for a given key value
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prevails.
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\subsection{String conversions}
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A string conversion is a condition list enclosed in {\em reverse} (or
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backward) quotes:
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\begin{verbatim}
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string_conversion: "`" condition_list "`"
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\end{verbatim}
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A string conversion evaluates the contained condition list and converts the
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resulting object into a string according to rules specific to its type.
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|
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If the object is a string, a number, \verb\None\, or a tuple, list or
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dictionary containing only objects whose type is in this list,
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the resulting
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string is a valid Python expression which can be passed to the
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built-in function \verb\eval()\ to yield an expression with the
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dictionary containing only objects whose type is one of these, the
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resulting string is a valid Python expression which can be passed to
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the built-in function \verb\eval()\ to yield an expression with the
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same value (or an approximation, if floating point numbers are
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involved).
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(In particular, converting a string adds quotes around it and converts
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``funny'' characters to escape sequences that are safe to print.)
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|
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It is illegal to attempt to convert recursive objects (e.g.,
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lists or dictionaries that -- directly or indirectly -- contain a reference
|
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to themselves.)
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It is illegal to attempt to convert recursive objects (e.g., lists or
|
||||
dictionaries that contain a reference to themselves, directly or
|
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indirectly.)
|
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\section{Primaries}
|
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|
@ -605,21 +681,73 @@ Primaries represent the most tightly bound operations of the language.
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Their syntax is:
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|
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\begin{verbatim}
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primary: atom | attributeref | call | subscription | slicing
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attributeref: primary "." identifier
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call: primary "(" [condition_list] ")"
|
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subscription: primary "[" condition "]"
|
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slicing: primary "[" [condition] ":" [condition] "]"
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primary: atom | attributeref | subscription | slicing | call
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\end{verbatim}
|
||||
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\subsection{Attribute references}
|
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\subsection{Calls}
|
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An attribute reference is a primary followed by a period and a name:
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|
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\begin{verbatim}
|
||||
attributeref: primary "." identifier
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\end{verbatim}
|
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|
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The primary must evaluate to an object of a type that supports
|
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attribute references, e.g., a module or a list. This object is then
|
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asked to produce the attribute whose name is the identifier. If this
|
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attribute is not available, the exception \verb\AttributeError\ is
|
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raised. Otherwise, the type and value of the object produced is
|
||||
determined by the object. Multiple evaluations of the same attribute
|
||||
reference may yield different objects.
|
||||
|
||||
\subsection{Subscriptions}
|
||||
|
||||
A subscription selects an item of a sequence or mapping object:
|
||||
|
||||
\begin{verbatim}
|
||||
subscription: primary "[" condition "]"
|
||||
\end{verbatim}
|
||||
|
||||
The primary must evaluate to an object of a sequence or mapping type.
|
||||
|
||||
If it is a mapping, the condition must evaluate to an object whose
|
||||
value is one of the keys of the mapping, and the subscription selects
|
||||
the value in the mapping that corresponds to that key.
|
||||
|
||||
If it is a sequence, the condition must evaluate to a nonnegative
|
||||
plain integer smaller than the number of items in the sequence, and
|
||||
the subscription selects the item whose index is that value (counting
|
||||
from zero).
|
||||
|
||||
A string's items are characters. A character is not a separate data
|
||||
type but a string of exactly one character.
|
||||
|
||||
\subsection{Slicings}
|
||||
|
||||
A slicing selects a range of items in a sequence object:
|
||||
|
||||
\begin{verbatim}
|
||||
slicing: primary "[" [condition] ":" [condition] "]"
|
||||
\end{verbatim}
|
||||
|
||||
XXX
|
||||
|
||||
\subsection{Calls}
|
||||
|
||||
A call calls a function with a possibly empty series of arguments:
|
||||
|
||||
\begin{verbatim}
|
||||
call: primary "(" [condition_list] ")"
|
||||
\end{verbatim}
|
||||
|
||||
The primary must evaluate to a callable object. Callable objects are
|
||||
user-defined functions, built-in functions, methods of built-in
|
||||
objects (``built-in methods''), class objects, and methods of class
|
||||
instances (``user-defined methods''). If it is a class, the argument
|
||||
list must be empty.
|
||||
|
||||
XXX explain what happens on function call
|
||||
|
||||
\section{Factors}
|
||||
|
||||
Factors represent the unary numeric operators.
|
||||
|
|
@ -634,7 +762,7 @@ The unary \verb\-\ operator yields the negative of its numeric argument.
|
|||
The unary \verb\+\ operator yields its numeric argument unchanged.
|
||||
|
||||
The unary \verb\~\ operator yields the bit-wise negation of its
|
||||
integral numerical argument.
|
||||
(plain or long) integral numerical argument, using 2's complement.
|
||||
|
||||
In all three cases, if the argument does not have the proper type,
|
||||
a {\tt TypeError} exception is raised.
|
||||
|
|
@ -647,27 +775,31 @@ Terms represent the most tightly binding binary operators:
|
|||
term: factor | term "*" factor | term "/" factor | term "%" factor
|
||||
\end{verbatim}
|
||||
|
||||
The \verb\*\ operator yields the product of its arguments.
|
||||
The arguments must either both be numbers, or one argument must be
|
||||
a (short) integer and the other must be a string.
|
||||
In the former case, the numbers are converted to a common type
|
||||
and then multiplied together.
|
||||
In the latter case, string repetition is performed; a negative
|
||||
repetition factor yields the empty string.
|
||||
The \verb\*\ (multiplication) operator yields the product of its
|
||||
arguments. The arguments must either both be numbers, or one argument
|
||||
must be a plain integer and the other must be a sequence. In the
|
||||
former case, the numbers are converted to a common type and then
|
||||
multiplied together. In the latter case, sequence repetition is
|
||||
performed; a negative repetition factor yields the empty string.
|
||||
|
||||
The \verb|"/"| operator yields the quotient of its arguments.
|
||||
The numeric arguments are first converted to a common type.
|
||||
(Short or long) integer division yields an integer of the same type,
|
||||
truncating towards zero.
|
||||
The \verb|"/"| (division) operator yields the quotient of its
|
||||
arguments. The numeric arguments are first converted to a common
|
||||
type. (Plain or long) integer division yields an integer of the same
|
||||
type; the result is that of mathematical division with the {\em floor}
|
||||
operator applied to the result, to match the modulo operator.
|
||||
Division by zero raises a {\tt RuntimeError} exception.
|
||||
|
||||
The \verb|"%"| operator yields the remainder from the division
|
||||
of the first argument by the second.
|
||||
The numeric arguments are first converted to a common type.
|
||||
The outcome of $x \% y$ is defined as $x - y*trunc(x/y)$.
|
||||
A zero right argument raises a {\tt RuntimeError} exception.
|
||||
The arguments may be floating point numbers, e.g.,
|
||||
$3.14 \% 0.7$ equals $0.34$.
|
||||
The \verb|"%"| (modulo) operator yields the remainder from the
|
||||
division of the first argument by the second. The numeric arguments
|
||||
are first converted to a common type. A zero right argument raises a
|
||||
{\tt RuntimeError} exception. The arguments may be floating point
|
||||
numbers, e.g., $3.14 \% 0.7$ equals $0.34$. The modulo operator
|
||||
always yields a result with the same sign as its second operand (or
|
||||
zero); the absolute value of the result is strictly smaller than the
|
||||
second operand.
|
||||
|
||||
The integer division and modulo operators are connected by the
|
||||
following identity: $x = (x/y)*y + (x\%y)$.
|
||||
|
||||
\section{Arithmetic expressions}
|
||||
|
||||
|
|
@ -675,12 +807,13 @@ $3.14 \% 0.7$ equals $0.34$.
|
|||
arith_expr: term | arith_expr "+" term | arith_expr "-" term
|
||||
\end{verbatim}
|
||||
|
||||
The \verb|"+"| operator yields the sum of its arguments.
|
||||
The arguments must either both be numbers, or both strings.
|
||||
In the former case, the numbers are converted to a common type
|
||||
and then added together.
|
||||
In the latter case, the strings are concatenated directly,
|
||||
without inserting a space.
|
||||
HIRO
|
||||
|
||||
The \verb|"+"| operator yields the sum of its arguments. The
|
||||
arguments must either both be numbers, or both sequences. In the
|
||||
former case, the numbers are converted to a common type and then added
|
||||
together. In the latter case, the sequences are concatenated
|
||||
directly.
|
||||
|
||||
The \verb|"-"| operator yields the difference of its arguments.
|
||||
The numeric arguments are first converted to a common type.
|
||||
|
|
@ -691,7 +824,7 @@ The numeric arguments are first converted to a common type.
|
|||
shift_expr: arith_expr | shift_expr "<<" arith_expr | shift_expr ">>" arith_expr
|
||||
\end{verbatim}
|
||||
|
||||
These operators accept short integers as arguments only.
|
||||
These operators accept (plain) integers as arguments only.
|
||||
They shift their left argument to the left or right by the number of bits
|
||||
given by the right argument. Shifts are ``logical"", e.g., bits shifted
|
||||
out on one end are lost, and bits shifted in are zero;
|
||||
|
|
@ -706,7 +839,7 @@ and_expr: shift_expr | and_expr "&" shift_expr
|
|||
\end{verbatim}
|
||||
|
||||
This operator yields the bitwise AND of its arguments,
|
||||
which must be short integers.
|
||||
which must be (plain) integers.
|
||||
|
||||
\section{Bitwise XOR expressions}
|
||||
|
||||
|
|
@ -715,7 +848,7 @@ xor_expr: and_expr | xor_expr "^" and_expr
|
|||
\end{verbatim}
|
||||
|
||||
This operator yields the bitwise exclusive OR of its arguments,
|
||||
which must be short integers.
|
||||
which must be (plain) integers.
|
||||
|
||||
\section{Bitwise OR expressions}
|
||||
|
||||
|
|
@ -724,7 +857,7 @@ or_expr: xor_expr | or_expr "|" xor_expr
|
|||
\end{verbatim}
|
||||
|
||||
This operator yields the bitwise OR of its arguments,
|
||||
which must be short integers.
|
||||
which must be (plain) integers.
|
||||
|
||||
\section{Expressions and expression lists}
|
||||
|
||||
|
|
|
|||
381
Doc/ref/ref.tex
381
Doc/ref/ref.tex
|
|
@ -49,7 +49,10 @@ informal introduction to the language, see the {\em Python Tutorial}.
|
|||
|
||||
\pagebreak
|
||||
|
||||
{
|
||||
\parskip = 0mm
|
||||
\tableofcontents
|
||||
}
|
||||
|
||||
\pagebreak
|
||||
|
||||
|
|
@ -84,6 +87,11 @@ standard modules. These are not documented here, but in the separate
|
|||
mentioned when they interact in a significant way with the language
|
||||
definition.
|
||||
|
||||
\section{Warning}
|
||||
|
||||
This version of the manual is incomplete. Sections that still need to
|
||||
be written or need considerable work are marked with ``XXX''.
|
||||
|
||||
\section{Notation}
|
||||
|
||||
The descriptions of lexical analysis and syntax use a modified BNF
|
||||
|
|
@ -150,7 +158,17 @@ Two or more physical lines may be joined into logical lines using
|
|||
backslash characters (\verb/\/), as follows: when a physical line ends
|
||||
in a backslash that is not part of a string literal or comment, it is
|
||||
joined with the following forming a single logical line, deleting the
|
||||
backslash and the following end-of-line character.
|
||||
backslash and the following end-of-line character. For example:
|
||||
%
|
||||
\begin{verbatim}
|
||||
samplingrates = (48000, AL.RATE_48000), \
|
||||
(44100, AL.RATE_44100), \
|
||||
(32000, AL.RATE_32000), \
|
||||
(22050, AL.RATE_22050), \
|
||||
(16000, AL.RATE_16000), \
|
||||
(11025, AL.RATE_11025), \
|
||||
( 8000, AL.RATE_8000)
|
||||
\end{verbatim}
|
||||
|
||||
\subsection{Blank lines}
|
||||
|
||||
|
|
@ -192,6 +210,9 @@ of Python code:
|
|||
|
||||
\begin{verbatim}
|
||||
def perm(l):
|
||||
|
||||
# Compute the list of all permutations of l
|
||||
|
||||
if len(l) <= 1:
|
||||
return [l]
|
||||
r = []
|
||||
|
|
@ -239,10 +260,9 @@ uppercase: "A"..."Z"
|
|||
digit: "0"..."9"
|
||||
\end{verbatim}
|
||||
|
||||
Identifiers are unlimited in length. Case is significant. Keywords
|
||||
are not identifiers.
|
||||
Identifiers are unlimited in length. Case is significant.
|
||||
|
||||
\section{Keywords}
|
||||
\subsection{Keywords}
|
||||
|
||||
The following identifiers are used as reserved words, or {\em
|
||||
keywords} of the language, and cannot be used as ordinary
|
||||
|
|
@ -322,8 +342,8 @@ but you may end up quadrupling backslashes that must appear literally.)
|
|||
|
||||
\subsection{Numeric literals}
|
||||
|
||||
There are three types of numeric literals: integers, long integers,
|
||||
and floating point numbers.
|
||||
There are three types of numeric literals: plain integers, long
|
||||
integers, and floating point numbers.
|
||||
|
||||
Integers and long integers are described by the following regular expressions:
|
||||
|
||||
|
|
@ -339,25 +359,43 @@ octdigit: "0"..."7"
|
|||
hexdigit: digit|"a"..."f"|"A"..."F"
|
||||
\end{verbatim}
|
||||
|
||||
Although both lower case `l'and upper case `L' are allowed as suffix
|
||||
for long integers, it is strongly recommended to always use `L', since
|
||||
the letter `l' looks too much like the digit `1'.
|
||||
|
||||
(Plain) integer decimal literals must be at most $2^{31} - 1$ (i.e., the
|
||||
largest positive integer, assuming 32-bit arithmetic); octal and
|
||||
hexadecimal literals may be as large as $2^{32} - 1$. There is no limit
|
||||
for long integer literals.
|
||||
|
||||
Some examples of (plain and long) integer literals:
|
||||
|
||||
\begin{verbatim}
|
||||
7 2147483647 0177 0x80000000
|
||||
3L 79228162514264337593543950336L 0377L 0100000000L
|
||||
\end{verbatim}
|
||||
|
||||
Floating point numbers are described by the following regular expressions:
|
||||
|
||||
\begin{verbatim}
|
||||
floatnumber: [intpart] fraction [exponent] | intpart ["."] exponent
|
||||
floatnumber: pointfloat | exponentfloat
|
||||
pointfloat: [intpart] fraction | intpart "."
|
||||
exponentfloat: (intpart | pointfloat) exponent
|
||||
intpart: digit+
|
||||
fraction: "." digit+
|
||||
exponent: ("e"|"E") ["+"|"-"] digit+
|
||||
\end{verbatim}
|
||||
|
||||
Some examples of numeric literals:
|
||||
The range of floating point literals is implementation-dependent.
|
||||
|
||||
Some examples of floating point literals:
|
||||
|
||||
\begin{verbatim}
|
||||
1 1234567890 0177777 0x80000
|
||||
|
||||
|
||||
3.14 10. .001 1e100 3.14e-10
|
||||
\end{verbatim}
|
||||
|
||||
Note that the definitions for literals do not include a sign; a phrase
|
||||
like \verb\-1\ is actually an expression composed of the operator
|
||||
Note that numeric literals do not include a sign; a phrase like
|
||||
\verb\-1\ is actually an expression composed of the operator
|
||||
\verb\-\ and the literal \verb\1\.
|
||||
|
||||
\section{Operators}
|
||||
|
|
@ -395,12 +433,6 @@ They may be used by future versions of the language though!
|
|||
|
||||
\chapter{Execution model}
|
||||
|
||||
(XXX This chapter should explain the general model of the execution of
|
||||
Python code and the evaluation of expressions. It should introduce
|
||||
objects, values, code blocks, scopes, name spaces, name binding,
|
||||
types, sequences, numbers, mappings, exceptions, and other technical
|
||||
terms needed to make the following chapters concise and exact.)
|
||||
|
||||
\section{Objects, values and types}
|
||||
|
||||
I won't try to define rigorously here what an object is, but I'll give
|
||||
|
|
@ -409,37 +441,41 @@ some properties of objects that are important to know about.
|
|||
Every object has an identity, a type and a value. An object's {\em
|
||||
identity} never changes once it has been created; think of it as the
|
||||
object's (permanent) address. An object's {\em type} determines the
|
||||
operations that an object supports (e.g., can its length be taken?)
|
||||
and also defines the ``meaning'' of the object's value; it also never
|
||||
changes. The {\em value} of some objects can change; whether an
|
||||
object's value can change is a property of its type.
|
||||
operations that an object supports (e.g., does it have a length?) and
|
||||
also defines the ``meaning'' of the object's value. The type also
|
||||
never changes. The {\em value} of some objects can change; whether
|
||||
this is possible is a property of its type.
|
||||
|
||||
Objects are never explicitly destroyed; however, when they become
|
||||
unreachable they may be garbage-collected. An implementation,
|
||||
however, is allowed to delay garbage collection or omit it altogether
|
||||
-- it is a matter of implementation quality how garbage collection is
|
||||
implemented. (Implementation note: the current implementation uses a
|
||||
unreachable they may be garbage-collected. An implementation is
|
||||
allowed to delay garbage collection or omit it altogether -- it is a
|
||||
matter of implementation quality how garbage collection is
|
||||
implemented, as long as no objects are collected that are still
|
||||
reachable. (Implementation note: the current implementation uses a
|
||||
reference-counting scheme which collects most objects as soon as they
|
||||
become onreachable, but does not detect garbage containing circular
|
||||
become onreachable, but never collects garbage containing circular
|
||||
references.)
|
||||
|
||||
Note that the use of the implementation's tracing or debugging
|
||||
facilities may keep objects alive that would normally be collectable.
|
||||
|
||||
(Some objects contain references to ``external'' resources such as
|
||||
open files. It is understood that these resources are freed when the
|
||||
object is garbage-collected, but since garbage collection is not
|
||||
guaranteed such objects also provide an explicit way to release the
|
||||
external resource (e.g., a \verb\close\ method) and programs are
|
||||
guaranteed, such objects also provide an explicit way to release the
|
||||
external resource (e.g., a \verb\close\ method). Programs are strongly
|
||||
recommended to use this.)
|
||||
|
||||
Some objects contain references to other objects. These references
|
||||
are part of the object's value; in most cases, when such a
|
||||
``container'' object is compared to another (of the same type), the
|
||||
comparison takes the {\em values} of the referenced objects into
|
||||
account (not their identities).
|
||||
comparison applies to the {\em values} of the referenced objects (not
|
||||
their identities).
|
||||
|
||||
Except for their identity, types affect almost any aspect of objects.
|
||||
Even object identities are affected in some sense: for immutable
|
||||
Types affect almost all aspects of objects.
|
||||
Even object identity is affected in some sense: for immutable
|
||||
types, operations that compute new values may actually return a
|
||||
reference to an existing object with the same type and value, while
|
||||
reference to any existing object with the same type and value, while
|
||||
for mutable objects this is not allowed. E.g., after
|
||||
|
||||
\begin{verbatim}
|
||||
|
|
@ -450,9 +486,13 @@ a = 1; b = 1; c = []; d = []
|
|||
\verb\c\ and \verb\d\ are guaranteed to refer to two different, unique,
|
||||
newly created lists.
|
||||
|
||||
\section{The standard type hierarchy}
|
||||
|
||||
XXX None, sequences, numbers, mappings, ...
|
||||
|
||||
\section{Execution frames, name spaces, and scopes}
|
||||
|
||||
XXX
|
||||
XXX code blocks, scopes, name spaces, name binding, exceptions
|
||||
|
||||
\chapter{Expressions and conditions}
|
||||
|
||||
|
|
@ -461,17 +501,17 @@ not lexical analysis.
|
|||
|
||||
This chapter explains the meaning of the elements of expressions and
|
||||
conditions. Conditions are a superset of expressions, and a condition
|
||||
may be used where an expression is required by enclosing it in
|
||||
parentheses. The only place where an unparenthesized condition is not
|
||||
allowed is on the right-hand side of the assignment operator, because
|
||||
this operator is the same token (\verb\=\) as used for compasisons.
|
||||
may be used wherever an expression is required by enclosing it in
|
||||
parentheses. The only places where expressions are used in the syntax
|
||||
instead of conditions is in expression statements and on the
|
||||
right-hand side of assignments; this catches some nasty bugs like
|
||||
accedentally writing \verb\x == 1\ instead of \verb\x = 1\.
|
||||
|
||||
The comma plays a somewhat special role in Python's syntax. It is an
|
||||
The comma has several roles in Python's syntax. It is usually an
|
||||
operator with a lower precedence than all others, but occasionally
|
||||
serves other purposes as well (e.g., it has special semantics in print
|
||||
statements). When a comma is accepted by the syntax, one of the
|
||||
syntactic categories \verb\expression_list\ or \verb\condition_list\
|
||||
is always used.
|
||||
serves other purposes as well; e.g., it separates function arguments,
|
||||
is used in list and dictionary constructors, and has special semantics
|
||||
in \verb\print\ statements.
|
||||
|
||||
When (one alternative of) a syntax rule has the form
|
||||
|
||||
|
|
@ -495,71 +535,89 @@ the following conversions are applied:
|
|||
the other is converted to floating point;
|
||||
\item else, if either argument is a long integer,
|
||||
the other is converted to long integer;
|
||||
\item otherwise, both must be short integers and no conversion
|
||||
\item otherwise, both must be plain integers and no conversion
|
||||
is necessary.
|
||||
\end{itemize}
|
||||
|
||||
(Note: ``short integers'' in Python are at least 32 bits in size;
|
||||
(Note: ``plain integers'' in Python are at least 32 bits in size;
|
||||
``long integers'' are arbitrary precision integers.)
|
||||
|
||||
\section{Atoms}
|
||||
|
||||
Atoms are the most basic elements of expressions.
|
||||
Forms enclosed in reverse quotes or various types of parentheses
|
||||
or braces are also categorized syntactically as atoms.
|
||||
Syntax rules for atoms:
|
||||
Atoms are the most basic elements of expressions. Forms enclosed in
|
||||
reverse quotes or in parentheses, brackets or braces are also
|
||||
categorized syntactically as atoms. The syntax for atoms is:
|
||||
|
||||
\begin{verbatim}
|
||||
atom: identifier | literal | parenth_form | string_conversion
|
||||
literal: stringliteral | integer | longinteger | floatnumber
|
||||
parenth_form: enclosure | list_display | dict_display
|
||||
enclosure: "(" [condition_list] ")"
|
||||
list_display: "[" [condition_list] "]"
|
||||
dict_display: "{" [key_datum ("," key_datum)* [","] "}"
|
||||
key_datum: condition ":" condition
|
||||
string_conversion:"`" condition_list "`"
|
||||
atom: identifier | literal | enclosure
|
||||
enclosure: parenth_form | list_display | dict_display | string_conversion
|
||||
\end{verbatim}
|
||||
|
||||
\subsection{Identifiers (Names)}
|
||||
|
||||
An identifier occurring as an atom is a reference to a local, global
|
||||
or built-in name binding. If a name can be assigned to anywhere in a code
|
||||
block, it refers to a local name throughout that code block.
|
||||
or built-in name binding. If a name can be assigned to anywhere in a
|
||||
code block, and is not mentioned in a \verb\global\ statement in that
|
||||
code block, it refers to a local name throughout that code block.
|
||||
Otherwise, it refers to a global name if one exists, else to a
|
||||
built-in name.
|
||||
|
||||
When the name is bound to an object, evaluation of the atom
|
||||
yields that object.
|
||||
When it is not bound, a {\tt NameError} exception
|
||||
is raised, with the identifier as string parameter.
|
||||
When the name is bound to an object, evaluation of the atom yields
|
||||
that object. When a name is not bound, an attempt to evaluate it
|
||||
raises a {\tt NameError} exception.
|
||||
|
||||
\subsection{Literals}
|
||||
|
||||
Python knows string and numeric literals:
|
||||
|
||||
\begin{verbatim}
|
||||
literal: stringliteral | integer | longinteger | floatnumber
|
||||
\end{verbatim}
|
||||
|
||||
Evaluation of a literal yields an object of the given type
|
||||
(string, integer, long integer, floating point number)
|
||||
with the given value.
|
||||
The value may be approximated in the case of floating point literals.
|
||||
|
||||
All literals correspond to immutable data types, and hence the object's
|
||||
identity is less important than its value.
|
||||
Multiple evaluations of the same literal (either the same occurrence
|
||||
in the program text or a different occurrence) may
|
||||
obtain the same object or a different object with the same value.
|
||||
All literals correspond to immutable data types, and hence the
|
||||
object's identity is less important than its value. Multiple
|
||||
evaluations of literals with the same value (either the same
|
||||
occurrence in the program text or a different occurrence) may obtain
|
||||
the same object or a different object with the same value.
|
||||
|
||||
(In the original implementation, all literals in the same code block
|
||||
with the same type and value yield the same object.)
|
||||
|
||||
\subsection{Enclosures}
|
||||
\subsection{Parenthesized form}
|
||||
|
||||
An empty enclosure yields an empty tuple object.
|
||||
A parenthesized form is an optional condition list enclosed in
|
||||
parentheses:
|
||||
|
||||
An enclosed condition list yields whatever that condition list yields.
|
||||
\begin{verbatim}
|
||||
parenth_form: "(" [condition_list] ")"
|
||||
\end{verbatim}
|
||||
|
||||
(Note that, except for empty tuples, tuples are not formed by
|
||||
enclosure in parentheses, but rather by use of the comma operator.)
|
||||
A parenthesized condition list yields whatever that condition list
|
||||
yields.
|
||||
|
||||
An empty pair of parentheses yields an empty tuple object (since
|
||||
tuples are immutable, the rules for literals apply here).
|
||||
|
||||
(Note that tuples are not formed by the parentheses, but rather by use
|
||||
of the comma operator. The exception is the empty tuple, for which
|
||||
parentheses {\em are} required -- allowing unparenthesized ``nothing''
|
||||
in expressions would causes ambiguities and allow common typos to
|
||||
pass uncaught.)
|
||||
|
||||
\subsection{List displays}
|
||||
|
||||
A list display is a possibly empty series of conditions enclosed in
|
||||
square brackets:
|
||||
|
||||
\begin{verbatim}
|
||||
list_display: "[" [condition_list] "]"
|
||||
\end{verbatim}
|
||||
|
||||
A list display yields a new list object.
|
||||
|
||||
If it has no condition list, the list object has no items.
|
||||
|
|
@ -568,36 +626,54 @@ from left to right and inserted in the list object in that order.
|
|||
|
||||
\subsection{Dictionary displays}
|
||||
|
||||
A dictionary display is a possibly empty series of key/datum pairs
|
||||
enclosed in curly braces:
|
||||
|
||||
\begin{verbatim}
|
||||
dict_display: "{" [key_datum_list] "}"
|
||||
key_datum_list: [key_datum ("," key_datum)* [","]
|
||||
key_datum: condition ":" condition
|
||||
\end{verbatim}
|
||||
|
||||
A dictionary display yields a new dictionary object.
|
||||
|
||||
The key/datum pairs are evaluated from left to right to
|
||||
define the entries of the dictionary:
|
||||
each key object is used as a key into the dictionary to store
|
||||
the corresponding datum pair.
|
||||
The key/datum pairs are evaluated from left to right to define the
|
||||
entries of the dictionary: each key object is used as a key into the
|
||||
dictionary to store the corresponding datum.
|
||||
|
||||
Keys must be strings, otherwise a {\tt TypeError} exception is raised.
|
||||
Clashes between keys are not detected; the last datum (textually
|
||||
rightmost in the display) stored for a given key value prevails.
|
||||
Keys must be strings, otherwise a {\tt TypeError} exception is raised.%
|
||||
\footnote{
|
||||
This restriction may be lifted in a future version of the language.
|
||||
}
|
||||
Clashes between duplicate keys are not detected; the last datum
|
||||
(textually rightmost in the display) stored for a given key value
|
||||
prevails.
|
||||
|
||||
\subsection{String conversions}
|
||||
|
||||
A string conversion is a condition list enclosed in {\em reverse} (or
|
||||
backward) quotes:
|
||||
|
||||
\begin{verbatim}
|
||||
string_conversion: "`" condition_list "`"
|
||||
\end{verbatim}
|
||||
|
||||
A string conversion evaluates the contained condition list and converts the
|
||||
resulting object into a string according to rules specific to its type.
|
||||
|
||||
If the object is a string, a number, \verb\None\, or a tuple, list or
|
||||
dictionary containing only objects whose type is in this list,
|
||||
the resulting
|
||||
string is a valid Python expression which can be passed to the
|
||||
built-in function \verb\eval()\ to yield an expression with the
|
||||
dictionary containing only objects whose type is one of these, the
|
||||
resulting string is a valid Python expression which can be passed to
|
||||
the built-in function \verb\eval()\ to yield an expression with the
|
||||
same value (or an approximation, if floating point numbers are
|
||||
involved).
|
||||
|
||||
(In particular, converting a string adds quotes around it and converts
|
||||
``funny'' characters to escape sequences that are safe to print.)
|
||||
|
||||
It is illegal to attempt to convert recursive objects (e.g.,
|
||||
lists or dictionaries that -- directly or indirectly -- contain a reference
|
||||
to themselves.)
|
||||
It is illegal to attempt to convert recursive objects (e.g., lists or
|
||||
dictionaries that contain a reference to themselves, directly or
|
||||
indirectly.)
|
||||
|
||||
\section{Primaries}
|
||||
|
||||
|
|
@ -605,21 +681,73 @@ Primaries represent the most tightly bound operations of the language.
|
|||
Their syntax is:
|
||||
|
||||
\begin{verbatim}
|
||||
primary: atom | attributeref | call | subscription | slicing
|
||||
attributeref: primary "." identifier
|
||||
call: primary "(" [condition_list] ")"
|
||||
subscription: primary "[" condition "]"
|
||||
slicing: primary "[" [condition] ":" [condition] "]"
|
||||
primary: atom | attributeref | subscription | slicing | call
|
||||
\end{verbatim}
|
||||
|
||||
\subsection{Attribute references}
|
||||
|
||||
\subsection{Calls}
|
||||
An attribute reference is a primary followed by a period and a name:
|
||||
|
||||
\begin{verbatim}
|
||||
attributeref: primary "." identifier
|
||||
\end{verbatim}
|
||||
|
||||
The primary must evaluate to an object of a type that supports
|
||||
attribute references, e.g., a module or a list. This object is then
|
||||
asked to produce the attribute whose name is the identifier. If this
|
||||
attribute is not available, the exception \verb\AttributeError\ is
|
||||
raised. Otherwise, the type and value of the object produced is
|
||||
determined by the object. Multiple evaluations of the same attribute
|
||||
reference may yield different objects.
|
||||
|
||||
\subsection{Subscriptions}
|
||||
|
||||
A subscription selects an item of a sequence or mapping object:
|
||||
|
||||
\begin{verbatim}
|
||||
subscription: primary "[" condition "]"
|
||||
\end{verbatim}
|
||||
|
||||
The primary must evaluate to an object of a sequence or mapping type.
|
||||
|
||||
If it is a mapping, the condition must evaluate to an object whose
|
||||
value is one of the keys of the mapping, and the subscription selects
|
||||
the value in the mapping that corresponds to that key.
|
||||
|
||||
If it is a sequence, the condition must evaluate to a nonnegative
|
||||
plain integer smaller than the number of items in the sequence, and
|
||||
the subscription selects the item whose index is that value (counting
|
||||
from zero).
|
||||
|
||||
A string's items are characters. A character is not a separate data
|
||||
type but a string of exactly one character.
|
||||
|
||||
\subsection{Slicings}
|
||||
|
||||
A slicing selects a range of items in a sequence object:
|
||||
|
||||
\begin{verbatim}
|
||||
slicing: primary "[" [condition] ":" [condition] "]"
|
||||
\end{verbatim}
|
||||
|
||||
XXX
|
||||
|
||||
\subsection{Calls}
|
||||
|
||||
A call calls a function with a possibly empty series of arguments:
|
||||
|
||||
\begin{verbatim}
|
||||
call: primary "(" [condition_list] ")"
|
||||
\end{verbatim}
|
||||
|
||||
The primary must evaluate to a callable object. Callable objects are
|
||||
user-defined functions, built-in functions, methods of built-in
|
||||
objects (``built-in methods''), class objects, and methods of class
|
||||
instances (``user-defined methods''). If it is a class, the argument
|
||||
list must be empty.
|
||||
|
||||
XXX explain what happens on function call
|
||||
|
||||
\section{Factors}
|
||||
|
||||
Factors represent the unary numeric operators.
|
||||
|
|
@ -634,7 +762,7 @@ The unary \verb\-\ operator yields the negative of its numeric argument.
|
|||
The unary \verb\+\ operator yields its numeric argument unchanged.
|
||||
|
||||
The unary \verb\~\ operator yields the bit-wise negation of its
|
||||
integral numerical argument.
|
||||
(plain or long) integral numerical argument, using 2's complement.
|
||||
|
||||
In all three cases, if the argument does not have the proper type,
|
||||
a {\tt TypeError} exception is raised.
|
||||
|
|
@ -647,27 +775,31 @@ Terms represent the most tightly binding binary operators:
|
|||
term: factor | term "*" factor | term "/" factor | term "%" factor
|
||||
\end{verbatim}
|
||||
|
||||
The \verb\*\ operator yields the product of its arguments.
|
||||
The arguments must either both be numbers, or one argument must be
|
||||
a (short) integer and the other must be a string.
|
||||
In the former case, the numbers are converted to a common type
|
||||
and then multiplied together.
|
||||
In the latter case, string repetition is performed; a negative
|
||||
repetition factor yields the empty string.
|
||||
The \verb\*\ (multiplication) operator yields the product of its
|
||||
arguments. The arguments must either both be numbers, or one argument
|
||||
must be a plain integer and the other must be a sequence. In the
|
||||
former case, the numbers are converted to a common type and then
|
||||
multiplied together. In the latter case, sequence repetition is
|
||||
performed; a negative repetition factor yields the empty string.
|
||||
|
||||
The \verb|"/"| operator yields the quotient of its arguments.
|
||||
The numeric arguments are first converted to a common type.
|
||||
(Short or long) integer division yields an integer of the same type,
|
||||
truncating towards zero.
|
||||
The \verb|"/"| (division) operator yields the quotient of its
|
||||
arguments. The numeric arguments are first converted to a common
|
||||
type. (Plain or long) integer division yields an integer of the same
|
||||
type; the result is that of mathematical division with the {\em floor}
|
||||
operator applied to the result, to match the modulo operator.
|
||||
Division by zero raises a {\tt RuntimeError} exception.
|
||||
|
||||
The \verb|"%"| operator yields the remainder from the division
|
||||
of the first argument by the second.
|
||||
The numeric arguments are first converted to a common type.
|
||||
The outcome of $x \% y$ is defined as $x - y*trunc(x/y)$.
|
||||
A zero right argument raises a {\tt RuntimeError} exception.
|
||||
The arguments may be floating point numbers, e.g.,
|
||||
$3.14 \% 0.7$ equals $0.34$.
|
||||
The \verb|"%"| (modulo) operator yields the remainder from the
|
||||
division of the first argument by the second. The numeric arguments
|
||||
are first converted to a common type. A zero right argument raises a
|
||||
{\tt RuntimeError} exception. The arguments may be floating point
|
||||
numbers, e.g., $3.14 \% 0.7$ equals $0.34$. The modulo operator
|
||||
always yields a result with the same sign as its second operand (or
|
||||
zero); the absolute value of the result is strictly smaller than the
|
||||
second operand.
|
||||
|
||||
The integer division and modulo operators are connected by the
|
||||
following identity: $x = (x/y)*y + (x\%y)$.
|
||||
|
||||
\section{Arithmetic expressions}
|
||||
|
||||
|
|
@ -675,12 +807,13 @@ $3.14 \% 0.7$ equals $0.34$.
|
|||
arith_expr: term | arith_expr "+" term | arith_expr "-" term
|
||||
\end{verbatim}
|
||||
|
||||
The \verb|"+"| operator yields the sum of its arguments.
|
||||
The arguments must either both be numbers, or both strings.
|
||||
In the former case, the numbers are converted to a common type
|
||||
and then added together.
|
||||
In the latter case, the strings are concatenated directly,
|
||||
without inserting a space.
|
||||
HIRO
|
||||
|
||||
The \verb|"+"| operator yields the sum of its arguments. The
|
||||
arguments must either both be numbers, or both sequences. In the
|
||||
former case, the numbers are converted to a common type and then added
|
||||
together. In the latter case, the sequences are concatenated
|
||||
directly.
|
||||
|
||||
The \verb|"-"| operator yields the difference of its arguments.
|
||||
The numeric arguments are first converted to a common type.
|
||||
|
|
@ -691,7 +824,7 @@ The numeric arguments are first converted to a common type.
|
|||
shift_expr: arith_expr | shift_expr "<<" arith_expr | shift_expr ">>" arith_expr
|
||||
\end{verbatim}
|
||||
|
||||
These operators accept short integers as arguments only.
|
||||
These operators accept (plain) integers as arguments only.
|
||||
They shift their left argument to the left or right by the number of bits
|
||||
given by the right argument. Shifts are ``logical"", e.g., bits shifted
|
||||
out on one end are lost, and bits shifted in are zero;
|
||||
|
|
@ -706,7 +839,7 @@ and_expr: shift_expr | and_expr "&" shift_expr
|
|||
\end{verbatim}
|
||||
|
||||
This operator yields the bitwise AND of its arguments,
|
||||
which must be short integers.
|
||||
which must be (plain) integers.
|
||||
|
||||
\section{Bitwise XOR expressions}
|
||||
|
||||
|
|
@ -715,7 +848,7 @@ xor_expr: and_expr | xor_expr "^" and_expr
|
|||
\end{verbatim}
|
||||
|
||||
This operator yields the bitwise exclusive OR of its arguments,
|
||||
which must be short integers.
|
||||
which must be (plain) integers.
|
||||
|
||||
\section{Bitwise OR expressions}
|
||||
|
||||
|
|
@ -724,7 +857,7 @@ or_expr: xor_expr | or_expr "|" xor_expr
|
|||
\end{verbatim}
|
||||
|
||||
This operator yields the bitwise OR of its arguments,
|
||||
which must be short integers.
|
||||
which must be (plain) integers.
|
||||
|
||||
\section{Expressions and expression lists}
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue