Boolean comparison & PEP8

[Terry Reedy]

On 7/28/2019 7:55 AM, Jonathan Moules wrote:

> Lets say I want to know if the value of `x` is bool(True).
> My preferred way to do it is:
> 
> if x is True:
>      pass

If you know that expression x is boolean, and one usually knows or 
should know whether is it or is not, '= True' and 'is True' and 
similarly for False are redundant.  Why not 'if x is True is True' and 
so on.

> Because this tests both the value and the type.

See below.

Newbies *have* written things like 'if (x == 3) is True' and this is 
what prompted this entry in PEP 8.

> """
> Don't compare boolean values to True or False using ==.
> 
> Yes:   if greeting:
> No:    if greeting == True:
> Worse: if greeting is True:
> """

> If `x` can also have a value of "1"(str) or 1(int) 

Have you run across any stdlib function that returns such a mixture of 
types?  Remember that PEP 8 is specifically a style guide for stdlib code.

-- 
Terry Jan Reedy