/Demo/classes/Rev.py
http://unladen-swallow.googlecode.com/ · Python · 95 lines · 93 code · 0 blank · 2 comment · 0 complexity · e8b6a62f19162bab884894634538e095 MD5 · raw 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()