Pythonic Swap?

Question

I found that i have to perform a swap in python and i write something like this.

arr[first], arr[second] = arr[second], arr[first]

I suppos

Answer 1

The one thing I might change in your example code: if you're going to use some long name such as self.memberlist over an over again, it's often more readable to alias ("assign") it to a shorter name first. So for example instead of the long, hard-to-read:

self.memberlist[someindexA], self.memberlist[someindexB] = self.memberlist[someindexB], self.memberlist[someindexA]

you could code:

L = self.memberlist
L[someindexA], L[someindexB] = L[someindexB], L[someindexA]

Remember that Python works by-reference so L refers to exactly the same object as self.memberlist, NOT a copy (by the same token, the assignment is extremely fast no matter how long the list may be, because it's not copied anyway -- it's just one more reference).

I don't think any further complication is warranted, though of course some fancy ones might easily be conceived, such as (for a, b "normal" indices >=0):

def slicer(a, b):
  return slice(a, b+cmp(b,a), b-a), slice(b, a+cmp(a,b), a-b)

back, forth = slicer(someindexA, someindexB)
self.memberlist[back] = self.memberlist[forth]

I think figuring out these kinds of "advanced" uses is a nice conceit, useful mental exercise, and good fun -- I recommend that interested readers, once the general idea is clear, focus on the role of those +cmp and how they make things work for the three possibilities (a>b, a

Remember, simple is better than complex!