Good code patterns in Python

[Terry Reedy]

"Will Stuyvesant" <hwlgw at hotmail.com> wrote in message
news:cb035744.0307010149.399df2eb at posting.google.com...
> If you know that your source code is going to be used
> later by others, then I feel that code with the pattern:
>
>     if some_condition:
>         some_name = some_value
>     else:
>         some_name = other_value
>
> is often a mistake.  Much better, safer, would be:
>
>     some_name = some_value
>     if not some_condition:
>         some_name = other_value

If, bool(some_value) == True, I personally would use the near-ternary
idiom

some_name = some_condition and some_value or other_value

(or equivalent form for bool(other_value)== True or either == False).

This is both safe and efficient, avoiding both

> Because those people reusing your code might decide to
> change or adapt the "if" part of the first example.  Or
> the "else" part for that matter.  And then they could end
> up with "some_name" being undefined, crashing other code
> maybe 1000's of lines away.

and

> There is the small overhead of assigning something twice

(I acknowledge that some think this ugly and worse and would not be
caught dead writing such an 'abomination', so flame repetition is not
necessary ;-)

Terry J. Reedy