[Tutor] List comprehension + lambdas - strange behaviour

[Ricardo Aráoz]

Artur Siekielski wrote:
> Hello.
> I found this strange behaviour of lambdas, closures and list
> comprehensions:
>
>   
>>>> funs = [lambda: x for x in range(5)]
>>>> [f() for f in funs]
>>>>         
> [4, 4, 4, 4, 4]
>
> Of course I was expecting the list [0, 1, 2, 3, 4] as the result. The
> 'x' was bound to the final value of 'range(5)' expression for ALL
> defined functions. Can you explain this? Is this only counterintuitive
> example or an error in CPython?
>
>
> Regards,
> Artur
>   
Check this :
>>> funs = [(lambda: x) for x in range(5)]
>>> funs[0]()
4
>>> x
4
>>> x = 3
>>> funs[0]()
3
>>> del x
>>> funs[0]()
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "<input>", line 1, in <lambda>
NameError: global name 'x' is not defined

So you see, your functions just return the value of x. That's because
the lambda have no parameter, so x refers to the global name x.

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