[Tutor] how to unittest cli input

[Steven D'Aprano]

On Mon, Oct 12, 2015 at 10:37:51AM -0700, Alex Kleider wrote:

> Any comments about when/if to use 'if src != None:' vs 'if src is not 
> None:'?
> (or 'if src == None:' vs 'if src is None:')

Short answer: always compare to None using `is` or `is not`.

Long answer:

If you want to check for src being specifically None, then use `src is 
None`, since None is the only object that can be identical to None.

If you want to check for some random object that merely compares equal 
to None (and why would you do that?) then use `src == None`, since that 
will give src a chance to decide whether or not it compares equal to 
None.

For built-in types (ints, floats, strings, etc.) there's no practical 
difference, but as soon as custom objects may be involved, then you 
don't know whether you might get some custom object that for reasons of 
its own will compare equal to None:

class Falsey:
    def __eq__(self, other):
        return (not other)


Also, `is` comparisons are faster than `==` comparisons, not that this 
will usually matter.


-- 
Steve