Add the iter() builtin to checker C407

[sauravsrijan]

iter()

Example:

even_iterator = iter([i for i in range(1,100) if i%2 == 0])

This can be directly written as:

even_iterator = iter(i for i in range(1,100) if i%2 == 0)

[adamchainz]

I think there might be a subtle change in the possible exceptions thrown as per #59

[adamchainz]

See also #58

[sauravsrijan]

Oh! Alright.

But for the existing cases in C407, why are they raised only for list comprehension?
Aren't they valid for different comprehensions too? example: set comprehension

[adamchainz]

They probably are, PR's welcome. If you make a PR please ensure you add a changelog note, update the documentation, and create tests.

[joaoe]

iter(<comprehension>) is redundant.
(<comprehension>) is enough and produces a generator.

[adamchainz]

You're right, since a generator is its own iterator:

In [3]: (x for x in range(1))
Out[3]: <generator object <genexpr> at 0x106df2e40>

In [4]: iter(x for x in range(1))
Out[4]: <generator object <genexpr> at 0x106df2eb0>

[adamchainz]

@sauravsrijan released a fix to your issue in version 3.2.0: https://pypi.org/project/flake8-comprehensions/3.2.0/

As per comments on #58 and #59, I'm closing this issue, since it's not generally safe due to the change in possible raised exception from IndexError to StopIteration.

[joaoe]

I'm closing this issue, since it's not generally safe due to the change in possible raised exception from IndexError to StopIteration.

#59 deals with <expr>[0]. This issue is just about a plain iter, which always raises a StopIteration when empty.

>>> next(iter([1 for _ in ""]))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration
>>> next(1 for _ in "")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

[adamchainz]

You're right!