author | Mike Kinghan <mikek@symbian.org> |
Thu, 25 Nov 2010 14:28:39 +0000 | |
branch | GCC_SURGE |
changeset 135 | 10852f1a0ae9 |
parent 1 | 2fb8b9db1c86 |
permissions | -rw-r--r-- |
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''' |
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A class which presents the reverse of a sequence without duplicating it. |
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From: "Steven D. Majewski" <sdm7g@elvis.med.virginia.edu> |
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It works on mutable or inmutable sequences. |
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>>> chars = list(Rev('Hello World!')) |
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>>> print ''.join(chars) |
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!dlroW olleH |
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The .forw is so you can use anonymous sequences in __init__, and still |
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keep a reference the forward sequence. ) |
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If you give it a non-anonymous mutable sequence, the reverse sequence |
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will track the updated values. ( but not reassignment! - another |
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good reason to use anonymous values in creating the sequence to avoid |
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confusion. Maybe it should be change to copy input sequence to break |
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the connection completely ? ) |
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>>> nnn = range(3) |
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>>> rnn = Rev(nnn) |
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>>> for n in rnn: print n |
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... |
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2 |
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1 |
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0 |
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>>> for n in range(4, 6): nnn.append(n) # update nnn |
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... |
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>>> for n in rnn: print n # prints reversed updated values |
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... |
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5 |
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4 |
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2 |
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1 |
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0 |
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>>> nnn = nnn[1:-1] |
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>>> nnn |
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[1, 2, 4] |
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>>> for n in rnn: print n # prints reversed values of old nnn |
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... |
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5 |
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4 |
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2 |
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1 |
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0 |
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# |
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>>> WH = Rev('Hello World!') |
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>>> print WH.forw, WH.back |
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Hello World! !dlroW olleH |
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>>> nnn = Rev(range(1, 10)) |
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>>> print nnn.forw |
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[1, 2, 3, 4, 5, 6, 7, 8, 9] |
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>>> print nnn.back |
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[9, 8, 7, 6, 5, 4, 3, 2, 1] |
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>>> rrr = Rev(nnn) |
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>>> rrr |
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<1, 2, 3, 4, 5, 6, 7, 8, 9> |
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|
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''' |
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class Rev: |
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def __init__(self, seq): |
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self.forw = seq |
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self.back = self |
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def __len__(self): |
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return len(self.forw) |
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def __getitem__(self, j): |
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return self.forw[-(j + 1)] |
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def __repr__(self): |
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seq = self.forw |
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if isinstance(seq, list): |
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wrap = '[]' |
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sep = ', ' |
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elif isinstance(seq, tuple): |
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wrap = '()' |
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sep = ', ' |
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elif isinstance(seq, str): |
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wrap = '' |
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sep = '' |
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else: |
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wrap = '<>' |
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sep = ', ' |
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outstrs = [str(item) for item in self.back] |
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return wrap[:1] + sep.join(outstrs) + wrap[-1:] |
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def _test(): |
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import doctest, Rev |
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return doctest.testmod(Rev) |
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if __name__ == "__main__": |
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_test() |