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Comment by qwph | Hacker News Reader

Interesting. It seems that (according to my Python prompt)

  x, y = 1, 2

and

  [x, y] = 1, 2

and even

  x, y = [1, 2]

are all identical in function. Are there any (subtle) distinctions between the three?

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The last is different in that it returns a list, not a tuple. This makes a difference if you want to change the object.

  >>> tuple = x, y = 1, 2
  >>> type(tuple)
  <type 'tuple'>
  >>> tuple
  (1, 2)
  >>> tuple[0] = 1
  Traceback (most recent call last):
    File "<stdin>", line 1, in ?
  TypeError: object doesn't support item assignment
  >>> lst = x, y = [1, 2]
  >>> type(lst)
  <type 'list'>
  >>> lst
  [1, 2]
  >>> lst[0] = 3
  >>> lst
  [3, 2]

Aha! There's actually no difference (i think) between:

1, 2

and:

(1, 2)

That seems to make sense.

I think that is true, but I think that it's only later versions of Python (2.5+, maybe?) that allow you to omit the parenthesis. I've had earlier versions (2.3?) complain of a syntax error when I leave them out.

I don't know if there are any higher level differences, but I suspect the pure tuple version (the first) would be a little faster.

Edit:

Nope! Up to randomness due to multitasking and paging, a benchmark on one million cases yields the same times, up to noise.

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