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Re: lambda - strange behavior

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  Re: lambda - strange behavior Chris Angelico <rosuav@gmail.com> - 2013-09-21 01:47 +1000

#54480 — Re: lambda - strange behavior

On Sat, Sep 21, 2013 at 1:21 AM, Kasper Guldmann <gmane@kalleguld.dk> wrote:
> f = []
> for n in range(5):
>     f.append( lambda x: x*n )

You're leaving n as a free variable here. The lambda function will
happily look to an enclosing scope, so this doesn't work. But there is
a neat trick you can do:

f = []
for n in range(5):
    f.append( lambda x,n=n: x*n )

You declare n as a second parameter, with a default value of the
current n. The two n's are technically completely separate, and one of
them is bound within the lambda.

BTW, any time you have a loop appending to a list, see if you can make
it a comprehension instead:

f = [lambda x,n=n: x*n for n in range(5)]

Often reads better, may execute better too.

ChrisA

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