Do not use len(SEQUENCE) to determine if a sequence is empty

[DimitriPapadopoulos]

From DeepSource.io:
Built-in function len used as condition PYL-C1802

Using the len function to check if a sequence is empty is not idiomatic and can be less performant than checking the truthiness of the object.

len doesn't know the context in which it is called, so if computing the length means traversing the entire sequence, it must; it doesn't know that the result is just being compared to 0. Computing the boolean value can stop after it sees the first element, regardless of how long the sequence actually is.

Addresses #2552 (comment).

[cclauss]

https://pypi.org/project/refurb (and probably other tools) can auto-discover these as FURB115

Some do not like this change because the current form makes it explicit that the object is a container and not merely a bool.

[larsoner]

In this case we know more than it just being a generic sequence, we know it's a list. So to me there's no real gain here. I think I'm with @cclauss's statement in the sense that we do actually lose a bit of information here, so -0.5 from me

[DimitriPapadopoulos]

No problem, in that case do not hesitate to close this PR.

[larsoner]

Thanks for the helpful discussions, but let's keep it explicit here!