[Python-ideas] PEP 572: Statement-Local Name Bindings

[Serhiy Storchaka]

28.02.18 16:06, Chris Angelico пише:
> On Thu, Mar 1, 2018 at 12:49 AM, Serhiy Storchaka <storchaka at gmail.com> wrote:
>> Other options:
>>
>>      g = (f(x) for x in range(5))
>>      stuff = [[y, y] for y in g]
> 
> That's the same as the one-liner, but with the genexp broken out. Not
> sure it helps much as examples go?

It is more readable. But can't be used as an expression.

>>      def g():
>>          for x in range(5):
>>              y = f(x)
>>              yield [y, y]
>>      stuff = list(g)
> 
> You're not the first to mention this, but I thought it basically
> equivalent to the "expand into a loop" form. Is it really beneficial
> to expand it, not just into a loop, but into a generator function that
> contains a loop?

It is slightly faster (if the list is not too small). It doesn't leak a 
temporary variable after loop. And in many cases you don't need a list, 
an iterator would work as well. In these cases it is easy to just drop 
calling list().