[SilurianWenlock]

Where are you meant to learn this?

[futureastronaut]

Python's list of built-in functions is fairly small https://docs.python.org/3/library/functions.html#built-in-fu... (but to be clear, I wouldn't ding somebody for forgetting about one of them).

[progval]

Reading other people's code (usually while improving it)

[xkcd-sucks]

https://docs.python.org/3/

Consider that your iterable may not be a list, and may not actually have a "length" prior to its being consumed