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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>
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