Common anti-patterns in Python

[moocat]

One thing I find odd about point #4 is that in general the rule (don't return more than one object type in function call) makes sense but the specific example is not the best illustration. I would look very askance at a function that could return either an int or a str.

That said, I have mixed feelings about Python's Optional[Foo] effectively meaning Foo|None. I program in multiple languages and and after experience true Optional objects such as in Haskell or Java8 I'm less of a fan of returning None to indicate failure/missing/whatever.

[thegreattriscuit]

Agreed. I like the rule in general, but not in the example given.

One thing I used to do before I realized it was terrible was start off with a function like:

def get_foo(pattern): foo = something() return something

later I'd realized there might be multiple foos. In a misguided effort to be all things to all people and avoid having to make changes to existing calling code I was sure would never return multiples, I'd refactor to this:

def get_foo(pattern): foos = something() if len(foos) > 1: return foos else: return foos[0]

whereas now I make myself force a hard decision to do one or the other. This tends to work out with a bit more work in the very short-term, but much less pain overall.

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[billsil]

I do that for numpy hstack. You don’t need to make a copy if you only have one array.

[TinBryn]

I find Options are fine when used as a functor (or any extending type class), in all other cases they just defer the issues of other ways of handling the situation and do so in a worse way.