mirror of
https://github.com/python/cpython.git
synced 2025-11-03 19:34:08 +00:00
95 lines
2 KiB
Python
Executable file
95 lines
2 KiB
Python
Executable file
'''
|
|
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.
|
|
|
|
>>> chars = list(Rev('Hello World!'))
|
|
>>> print ''.join(chars)
|
|
!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(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
|
|
Hello World! !dlroW olleH
|
|
>>> nnn = Rev(range(1, 10))
|
|
>>> print nnn.forw
|
|
[1, 2, 3, 4, 5, 6, 7, 8, 9]
|
|
>>> print nnn.back
|
|
[9, 8, 7, 6, 5, 4, 3, 2, 1]
|
|
|
|
>>> rrr = Rev(nnn)
|
|
>>> rrr
|
|
<1, 2, 3, 4, 5, 6, 7, 8, 9>
|
|
|
|
'''
|
|
|
|
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 isinstance(seq, list):
|
|
wrap = '[]'
|
|
sep = ', '
|
|
elif isinstance(seq, tuple):
|
|
wrap = '()'
|
|
sep = ', '
|
|
elif isinstance(seq, str):
|
|
wrap = ''
|
|
sep = ''
|
|
else:
|
|
wrap = '<>'
|
|
sep = ', '
|
|
outstrs = [str(item) for item in self.back]
|
|
return wrap[:1] + sep.join(outstrs) + wrap[-1:]
|
|
|
|
def _test():
|
|
import doctest, Rev
|
|
return doctest.testmod(Rev)
|
|
|
|
if __name__ == "__main__":
|
|
_test()
|