[Tutor] how to unittest cli input

[Ben Finney]

Alex Kleider <akleider at sonic.net> writes:

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

Express your intention in the code.

If you want to express “is this value the ‘None’ singleton?”, compare
identity with ‘is’/‘is not’. (This is what you almost always mean when
comparing to ‘None’; I know of no useful exceptions to this.)

If you want to express “is this value possibly different from ‘None’ but
compares as equal?”, compare for equality with ‘==’/‘!=’. (As can be
guessed from my description, I don't know of any good reason this would
be preferred for ‘None’.)

The distinction gets to the issue of object identity, as distinct from
value equality. You don't need to know the details of that quite yet.

Just know that you can choose whether to allow an object to declare it
is equal to some other value, without actually being that same value.
That's what you want in most comparisons (use ‘==’), but there is a
large minority of comparisons where you instead want to know whether an
object *is* some other object (use ‘is’).

-- 
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Ben Finney