cpython/Tools/freeze

THE FREEZE SCRIPT
=================


What is Freeze?
---------------

Freeze make it possible to ship arbitrary Python programs to people
who don't have Python.  The shipped file (called a "frozen" version of
your Python program) is an executable, so this only works if your
platform is compatible with that on the receiving end (this is usually
a matter of having the same major operating system revision and CPU
type).

The shipped file contains a Python interpreter and large portions of
the Python run-time.  Some measures have been taken to avoid linking
unneeded modules, but the resulting binary is usually not small.

The Python source code of your program (and of the library modules
written in Python that it uses) is not included in the binary --
instead, the compiled byte-code (the instruction stream used
internally by the interpreter) is incorporated.  This gives some
protection of your Python source code, though not much -- a
disassembler for Python byte-code is available in the standard Python
library.  At least someone running "strings" on your binary won't see
the source.


How does Freeze know which modules to include?
----------------------------------------------

Freeze uses a pretty simple-minded algorithm to find the modules that
your program uses: given a file containing Python source code, it
scans for lines beginning with the word "import" or "from" (possibly
preceded by whitespace) and then it knows where to find the module
name(s) in those lines.  It then recursively scans the source for
those modules (if found, and not already processed) in the same way.

Freeze will not see import statements hidden behind another statement,
like this:

	if some_test: import M  # M not seen

or like this:

	import A; import B; import C  # B and C not seen

nor will it see import statements constructed using string
operations and passed to 'exec', like this:

	exec "import %s" % "M"  # M not seen

On the other hand, Freeze will think you are importing a module even
if the import statement it sees will never be executed, like this:

	if 0:
		import M  # M is seen

One tricky issue: Freeze assumes that the Python interpreter and
environment you're using to run Freeze is the same one that would be
used to run your program, which should also be the same whose sources
and installed files you will learn about in the next section.  In
particular, your PYTHONPATH setting should be the same as for running
your program locally.  (Tip: if the program doesn't run when you type
"python hello.py" there's little chance of getting the frozen version
to run.)


How do I use Freeze?
--------------------

Ideally, you should be able to use it as follows:

	python freeze.py hello.py

where hello.py is your program and freeze.py is the main file of
Freeze (in actuality, you'll probably specify an absolute pathname
such as /ufs/guido/src/python/Tools/freeze/freeze.py).

Unfortunately, this doesn't work.  Well, it might, but somehow it's
extremely unlikely that it'll work on the first try.  (If it does,
skip to the next section.)  Most likely you'll get this error message:

	needed directory /usr/local/lib/python/lib not found

The reason is that Freeze require that some files that are normally
kept inside the Python build tree are installed, and it searches for
it in the default install location.  (The default install prefix is
/usr/local; these particular files are installed at lib/python/lib
under the install prefix.)

The particular set of files needed is installed only if you run "make
libainstall" (note: "liba", not "lib") in the Python build tree (which
is the tree where you build Python -- often, but not necessarily, this
is also the Python source tree).  If you have in fact done a "make
libainstall" but used a different prefix, all you need to do is pass
that same prefix to Freeze with the -p option:

	python freeze.py -p your-prefix hello.py

If you haven't run "make libainstall" yet, you should do it now
(perhaps figuring out first *where* you want everything to be
installed).


How do I configure Freeze?
--------------------------

It's a good idea to change the first line marked with XXX in freeze.py
(an assignment to variable PACK) to point to the absolute pathname of
the directory where Freeze lives (Tools/freeze in the Python source
tree.)  This makes it possible to call Freeze from other directories.

You can also edit the assignment to variable PREFIX (also marked with
XXX) -- this saves a lot of -p options.


How do I use Freeze with extensions modules?
--------------------------------------------

XXX to be written.  (In short: pass -e extensionbuilddir.)


How do I use Freeze with dynamically loaded extension modules?
--------------------------------------------------------------

XXX to be written.  (In short: pass -e modulebuilddir -- this even
works if you built the modules in Python's own Modules directory.)


What do I do next?
------------------

Freeze creates three files: frozen.c, config.c and Makefile.  To
produce the frozen version of your program, you can simply type
"make".  This should produce a binary file.  If the filename argument
to Freeze was "hello.py", the binary will be called "hello".  On the
other hand, if the argument was "hello", the binary will be called
"hello.bin".  If you passed any other filename, all bets are off. :-)
In any case, the name of the file will be printed as the last message
from Freeze.


Troubleshooting
---------------

If you have trouble using Freeze for a large program, it's probably
best to start playing with a really simple program first (like the
file hello.py).  If you can't get that to work there's something
fundamentally wrong -- read the text above to find out how to install
relevant parts of Python properly and how to configure Freeze to find
them.

A common problem is having installed an old version -- rerunning "make
libainstall" often clears up problems with missing modules or
libraries at link time.


What is nfreeze.py?
-------------------

The script nfreeze.py is an unsupported variant on freeze.py which
creates all files in a temporary directory and runs "make" there.  It
has the advantage that it doesn't overwrite files in the current
directory, but the disadvantage is that it removes all files when it
is finished.


--Guido van Rossum, CWI, Amsterdam <mailto:Guido.van.Rossum@cwi.nl>
<http://www.cwi.nl/cwi/people/Guido.van.Rossum.html>