Re: What does a list comprehension do

From	Marko Rauhamaa <marko@pacujo.net>
Newsgroups	comp.lang.python
Subject	Re: What does a list comprehension do
Date	2015-11-26 15:56 +0200
Organization	A noiseless patient Spider
Message-ID	<87fuzseuee.fsf@elektro.pacujo.net> (permalink)
References	(2 earlier) <mailman.73.1448459485.20593.python-list@python.org> <pan.2015.11.26.11.13.43.440000@nowhere.invalid> <mailman.132.1448538769.20593.python-list@python.org> <87k2p4ex5x.fsf@elektro.pacujo.net> <mailman.138.1448544914.20593.python-list@python.org>

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Antoon Pardon <antoon.pardon@rece.vub.ac.be>:

> I don't understand. What I propose would be a minor change in
> how list comprehension works. I don't see how your example
> can be turned into a list comprehension.

The list comprehension is only a special case of the interaction between
closures and variables. If you dabble with list comprehensions and
lambdas, you'll need to make consistent changes in closure semantics.

That would lead to the trouble I mentioned. Closures need to have
dynamic access to the variables they refer to.

This whole issue is a consequence of Python's assignment semantics. If
Python didn't allow altering the values of variables, we wouldn't be
having this discussion.

BTW, all(!?) other languages from Java to Scheme share closure semantics
with Python so you would really be making a mess by changing Python.


Marko

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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