Re: What does a list comprehension do

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From	Antoon Pardon <antoon.pardon@rece.vub.ac.be>
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Subject	Re: What does a list comprehension do
Date	Thu, 26 Nov 2015 12:52:45 +0100
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Op 26-11-15 om 12:13 schreef Nobody:
> Returning to the original expression:
>
> 	> q = [lambda x: i * x for i in range(4)]
> 	> q[0](1), q[3](1)
> 	(3, 3)
> 	> q = [lambda x,i=i: i * x for i in range(4)]
> 	> q[0](1), q[3](1)
> 	(0, 3)

Personnaly I would prefer:

>>> q = [(lambda i: lambda x: i * x)(i) for i in range(4)]
>>> q[0](1), q[3](1)
(0, 3)

And this is where I ask whether it would be worth the effort to change
the behaviour of python.

In general the following two seem equivallent:

   [<expression> for x in <iter>] and [(lambda x: <expression>)(x) for x in <iter>]

The only exceptions seems to be when <expression> is itself a lambda.

It also seems that people who try this for the first time are surprised
with what they get and seem to expect there list comprehension to
act as if they had written the second version.

So would it be advisable if python would translate the expression people
write into a lambda that gets called?

Are there issues that could come up?

Thread

What does a list comprehension do (was: Late-binding of function defaults (was Re: What is a function parameter =[] for?)) Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-25 14:51 +0100
  Re: What does a list comprehension do (was: Late-binding of function defaults (was Re: What is a function parameter =[] for?)) Nobody <nobody@nowhere.invalid> - 2015-11-26 11:13 +0000
    Re: What does a list comprehension do Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-26 12:52 +0100
      Re: What does a list comprehension do Marko Rauhamaa <marko@pacujo.net> - 2015-11-26 14:56 +0200
        Re: What does a list comprehension do Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-26 14:33 +0100
          Re: What does a list comprehension do Marko Rauhamaa <marko@pacujo.net> - 2015-11-26 15:56 +0200
            Re: What does a list comprehension do Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-26 15:26 +0100
              Re: What does a list comprehension do Marko Rauhamaa <marko@pacujo.net> - 2015-11-26 17:36 +0200
                Re: What does a list comprehension do Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-26 20:18 +0100
              Re: What does a list comprehension do Jussi Piitulainen <harvest@is.invalid> - 2015-11-26 18:11 +0200

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