Mercurial > cpython-lru_cache-weakref

annotate Demo/classes/Rev.py @ 79675:c0a2294de787 2.7

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Issue #16199: Backport 2to3 typo fix from 3.2.
author Chris Jerdonek <chris.jerdonek@gmail.com>
date Thu, 11 Oct 2012 16:15:46 -0700
parents b8737a31050c
children b0743d52b6a3
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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1 '''
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2 A class which presents the reverse of a sequence without duplicating it.
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3 From: "Steven D. Majewski" <sdm7g@elvis.med.virginia.edu>
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4
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5 It works on mutable or inmutable sequences.
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6
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7 >>> chars = list(Rev('Hello World!'))
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8 >>> print ''.join(chars)
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9 !dlroW olleH
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10
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11 The .forw is so you can use anonymous sequences in __init__, and still
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12 keep a reference the forward sequence. )
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13 If you give it a non-anonymous mutable sequence, the reverse sequence
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14 will track the updated values. ( but not reassignment! - another
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15 good reason to use anonymous values in creating the sequence to avoid
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16 confusion. Maybe it should be change to copy input sequence to break
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17 the connection completely ? )
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18
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19 >>> nnn = range(3)
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20 >>> rnn = Rev(nnn)
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21 >>> for n in rnn: print n
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22 ...
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23 2
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24 1
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25 0
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26 >>> for n in range(4, 6): nnn.append(n) # update nnn
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27 ...
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28 >>> for n in rnn: print n # prints reversed updated values
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29 ...
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30 5
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31 4
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32 2
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33 1
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34 0
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35 >>> nnn = nnn[1:-1]
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36 >>> nnn
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37 [1, 2, 4]
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38 >>> for n in rnn: print n # prints reversed values of old nnn
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39 ...
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40 5
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41 4
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42 2
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43 1
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44 0
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45
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46 #
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47 >>> WH = Rev('Hello World!')
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48 >>> print WH.forw, WH.back
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49 Hello World! !dlroW olleH
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50 >>> nnn = Rev(range(1, 10))
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51 >>> print nnn.forw
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52 [1, 2, 3, 4, 5, 6, 7, 8, 9]
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53 >>> print nnn.back
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54 [9, 8, 7, 6, 5, 4, 3, 2, 1]
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55
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56 >>> rrr = Rev(nnn)
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57 >>> rrr
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58 <1, 2, 3, 4, 5, 6, 7, 8, 9>
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59
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60 '''
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61
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62 class Rev:
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63 def __init__(self, seq):
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64 self.forw = seq
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65 self.back = self
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66
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67 def __len__(self):
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68 return len(self.forw)
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69
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70 def __getitem__(self, j):
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71 return self.forw[-(j + 1)]
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72
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73 def __repr__(self):
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74 seq = self.forw
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75 if isinstance(seq, list):
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76 wrap = '[]'
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77 sep = ', '
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78 elif isinstance(seq, tuple):
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79 wrap = '()'
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80 sep = ', '
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81 elif isinstance(seq, str):
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82 wrap = ''
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83 sep = ''
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84 else:
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85 wrap = '<>'
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86 sep = ', '
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87 outstrs = [str(item) for item in self.back]
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88 return wrap[:1] + sep.join(outstrs) + wrap[-1:]
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89
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90 def _test():
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91 import doctest, Rev
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92 return doctest.testmod(Rev)
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93
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94 if __name__ == "__main__":
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95 _test()