"[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote in
news:[EMAIL PROTECTED]:
>
> Shi Mu wrote:
>> what does the following code mean? It is said to be used in the
>> calculation of the overlaid area size between two polygons.
>> map(lambda x:b.setdefault(x,[]),a)
>
> The equivalent of :
>
> def oh_my_yet_another_function_name_why_not_use_lambda(x):
> b.setdefault(x,[])
>
> map(oh_my_yet_another_function_name_why_not_use_lambda, a)
>
> Or
>
> for x in a:
> b.setdefault(x,[])
>
>
Or even:
[b.setdefault(x,[]) for x in a]
The effect of the code is this: if you have b, a dictionary of
values, and a, a list or tuple of indexes to the dictionary, you
can generate a list that will contain just the values associated
with the indices in the list. If the index is not found in the
dictionary, the default value will be used; in this case, that is
an empty list.
So, for example, if you have
b = {'x':1,1:(1,2,3),'arthur':'A string',99:{'j':45,'k':111}}
and a looks like this: you produce this:
a = (0,1,'x') [[], (1, 2, 3), 1]
a = (0,2,3,22) [[], [], [], []]
a = ['x','arthur'] [1, 'A string']
... and so on.
--
rzed
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