mirror of https://github.com/python/cpython.git
90 lines
2.0 KiB
Python
90 lines
2.0 KiB
Python
|
# A class which presents the reverse of a sequence without duplicating it.
|
||
|
|
# From: "Steven D. Majewski" <sdm7g@elvis.med.virginia.edu>
|
||
|
|
|
||
|
|
# It works on mutable or inmutable sequences.
|
||
|
|
#
|
||
|
|
# >>> for c in Rev( 'Hello World!' ) : sys.stdout.write( c )
|
||
|
|
# ... else: sys.stdout.write( '\n' )
|
||
|
|
# ...
|
||
|
|
# !dlroW olleH
|
||
|
|
#
|
||
|
|
# The .forw is so you can use anonymous sequences in init, and still
|
||
|
|
# keep a reference the forward sequence. )
|
||
|
|
# If you give it a non-anonymous mutable sequence, the reverse sequence
|
||
|
|
# will track the updated values. ( but not reassignment! - another
|
||
|
|
# good reason to use anonymous values in creating the sequence to avoid
|
||
|
|
# confusion. Maybe it should be change to copy input sequence to break
|
||
|
|
# the connection completely ? )
|
||
|
|
#
|
||
|
|
# >>> nnn = range( 0, 3 )
|
||
|
|
# >>> rnn = Rev( nnn )
|
||
|
|
# >>> for n in rnn: print n
|
||
|
|
# ...
|
||
|
|
# 2
|
||
|
|
# 1
|
||
|
|
# 0
|
||
|
|
# >>> for n in range( 4, 6 ): nnn.append( n ) # update nnn
|
||
|
|
# ...
|
||
|
|
# >>> for n in rnn: print n # prints reversed updated values
|
||
|
|
# ...
|
||
|
|
# 5
|
||
|
|
# 4
|
||
|
|
# 2
|
||
|
|
# 1
|
||
|
|
# 0
|
||
|
|
# >>> nnn = nnn[1:-1]
|
||
|
|
# >>> nnn
|
||
|
|
# [1, 2, 4]
|
||
|
|
# >>> for n in rnn: print n # prints reversed values of old nnn
|
||
|
|
# ...
|
||
|
|
# 5
|
||
|
|
# 4
|
||
|
|
# 2
|
||
|
|
# 1
|
||
|
|
# 0
|
||
|
|
# >>>
|
||
|
|
#
|
||
|
|
# WH = Rev( 'Hello World!' )
|
||
|
|
# print WH.forw, WH.back
|
||
|
|
# nnn = Rev( range( 1, 10 ) )
|
||
|
|
# print nnn.forw
|
||
|
|
# print nnn
|
||
|
|
#
|
||
|
|
# produces output:
|
||
|
|
#
|
||
|
|
# Hello World! !dlroW olleH
|
||
|
|
# [1, 2, 3, 4, 5, 6, 7, 8, 9]
|
||
|
|
# [9, 8, 7, 6, 5, 4, 3, 2, 1]
|
||
|
|
#
|
||
|
|
# >>>rrr = Rev( nnn )
|
||
|
|
# >>>rrr
|
||
|
|
# <1, 2, 3, 4, 5, 6, 7, 8, 9>
|
||
|
|
|
||
|
|
from string import joinfields
|
||
|
|
class Rev:
|
||
|
|
def __init__( self, seq ):
|
||
|
|
self.forw = seq
|
||
|
|
self.back = self
|
||
|
|
def __len__( self ):
|
||
|
|
return len( self.forw )
|
||
|
|
def __getitem__( self, j ):
|
||
|
|
return self.forw[ -( j + 1 ) ]
|
||
|
|
def __repr__( self ):
|
||
|
|
seq = self.forw
|
||
|
|
if type(seq) == type( [] ) :
|
||
|
|
wrap = '[]'
|
||
|
|
sep = ', '
|
||
|
|
elif type(seq) == type( () ) :
|
||
|
|
wrap = '()'
|
||
|
|
sep = ', '
|
||
|
|
elif type(seq) == type( '' ) :
|
||
|
|
wrap = ''
|
||
|
|
sep = ''
|
||
|
|
else:
|
||
|
|
wrap = '<>'
|
||
|
|
sep = ', '
|
||
|
|
outstrs = []
|
||
|
|
for item in self.back :
|
||
|
|
outstrs.append( str( item ) )
|
||
|
|
return wrap[:1] + joinfields( outstrs, sep ) + wrap[-1:]
|