python中的这个旋转程序怎么了？

Question

context: (enigma machine) What I am trying to do is get this bit of code to run so that the first wheel will rotate each time the sequences goes through the first wheel.

The problem is that i worked out how to do the rotation using a this sequences below from the internet yet it is not working when I change the variables around so that it can be auto-mated more. It comes up with error messages after the if function. I have checked through and changed the names of the variables to make them simpler and the spacing. And can't find out whats not working in the code. For is it that the rotate function can't use variables or what?

import collections

theinput=raw_input('enter letter')
x=0



w=collections.ww=([1,2,3,4,5])


if theinput == 'a':
    w.rotate(x)
    a = w[0]
    x= x+1
    w.rotate(x)
 print a

Thanks

Answer 1

The container you probably want to use is deque , as far as I know there is no such variable as ww in collections module.

To put a bit of context, a deque is very similar to a list, but it is optimized in such a way that you can easily (efficiently) add and remove items at both ends, which is slightly more efficient that for built-in lists. Also deques provides some additional methods not found in lists, like rotate. While it's really easy to do the same things with lists combining basic operations, they are not optimized for these kind of things, while deques are. But for something as simple as simulation of an Enigma machine, sticking with lists wouldn't change performance much anyway.

I guess you are trying to do something like:

import collections
w = collections.deque([1, 2, 3, 4, 5])
print "Deque state is ", w
print "First item in deque is", w[0]
w.rotate(1)
print "Deque state after rotation is ", w
print "First item in deque is", w[0]

This should print

Deque state is  deque([1, 2, 3, 4, 5])
First item in deque is 1 Deque
state after rotation is  deque([5, 1, 2, 3, 4])
First item in deque is 5

Use negative numbers as arguments for rotate to turn the other way

Below is an alternative implementation using only built-in lists

w = [1, 2, 3, 4, 5]
print "List state is ", w
print "First item in list is", w[0]
x = 1 # x is rotation
w0 = w[:-x]
w = w[-x:]
w.extend(w0)
print "List state after rotation is ", w
print "First item in list is", w[0]