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pythondeque

Python: Deque[-1] = Deque.pop() giving interesting result

I was working with a deque and was wondering why the following code works the way it does Code:

import collections

d = collections.deque()
d.append("a")
d.append("b")
d[-1] += d.pop()
print(d)

Output: deque(['bb'])

This surprised me, as I would have expected the code to result in deque(['ab']) instead of deque(['bb']). Why did this occur?

Solution

  • this line

    d[-1] += d.pop()

    is equal by this line

    d[-1] = d[-1] + d.pop()

    python first get d[-1] and that is 'b'

    after that run pop method for d and this method return 'b' at the end python set 'bb' for d[-1]

    if you want pop first item use popleft() function.

    edited code:

    from collections import deque


d = deque()

d.append("a")
d.append("b")

d[-1] = d.popleft() + d[-1]

print(d)

    output:

    deque(['ab'])