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