Expression can be simplified on list

[Thomas 'PointedEars' Lahn]

Chris Angelico wrote:

> On Mon, Sep 12, 2016 at 9:14 PM, Daiyue Weng <daiyueweng at gmail.com> wrote:
>> Hi, I found that when I tried to make an equality test on empty like,
>>
>> if errors == []:
>>
>> PyCharm always warns me,
>>
>> Expression can be simplified.
>>
>> I am wondering what's wrong and how to fix this?
>>
> 
> If you know that 'errors' is always going to be a list, you can check
> for emptiness thus:
> 
> if not errors:

If I knew that it is always going to be a list or a tuple, I would check its 
length instead:

  if len(errors) == 0:

Only if I did not know that I would use the “not” keyword, because the 
latter

  a) forces a type conversion to “bool”;
  b) also works with values of other types.
 
> PyCharm recommends this syntax rather than the comparison with a
                     ^^^^^^^^^^^
> newly-created empty list.

Are you sure?

> Your code has to actually construct and dispose of a list, just for the
> comparison.

ACK

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PointedEars

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