Paddy schrieb:
Iam wondering why the peculiar behavior of map when the function in
given as None:
Help on built-in function map in module __builtin__:
map(...)
map(function, sequence[, sequence, ...]) -> list
Return a list of the results of applying the function to the items
of
the argument sequence(s). If more than one sequence is given, the
function is called with an argument list consisting of the
corresponding
item of each sequence, substituting None for missing values when
not all
sequences have the same length. If the function is None, return a
list of
the items of the sequence (or a list of tuples if more than one
sequence).
It seems as the action whith none is the same as using a function of
lambda *x: x
As in the following example:
l1 = 'asdf'
l2 = 'qwertyuip'
l3 = range(3)
l1,l2,l3
('asdf', 'qwertyuip', [0, 1, 2])
map(lambda *x: x, l1,l2,l3) == map(None, l1,l2,l3)
True
On looking up map on Wikipedia there is no mention of this special
behaviour,
So my question is why?
Because it is undefined what should happen in case of no function given
at all - and because there is no identity function in python
pre-defined, it could be considered sensible to make None the quivalent
of that function.
And it only follows that *if* you imply a function even though there is
None given, that the passed tuple is returned.
I don't see anything on wikipedia that defines any other behavior.
Diez
Diez
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