In Python one can do:
a, b = 1, 2 (a, b) = 1, 2 [a, b] = 1, 2
I checked the generated bytecode using dis
and they are identical.
So why allow this at all? Would I ever need one of these instead of the others?
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Answer
One case when you need to include more structure on the left hand side of the assignment is when you’re asking Python unpack a slightly more complicated sequence. E.g.:
# Works >>> a, (b, c) = [1, [2, 3]] # Does not work >>> a, b, c = [1, [2, 3]] Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: need more than 2 values to unpack
This has proved useful for me in the past, for example, when using enumerate to iterate over a sequence of 2-tuples. Something like:
>>> d = { 'a': 'x', 'b': 'y', 'c': 'z' } >>> for i, (key, value) in enumerate(d.iteritems()): ... print (i, key, value) (0, 'a', 'x') (1, 'c', 'z') (2, 'b', 'y')