No. I put that in places where I receive a generator and want a list. But, there are plenty of instances of what you're talking about. Take a look at the stan

No. I put that in places where I receive a generator and want a list. But, there are plenty of instances of what you're talking about. Take a look at the standard library. Itertools often creates an iterator as the first operation, not knowing whether it received an iterator or some other kind of iterable. https://github.com/python/cpython/blob/384621c42f9102e31ba2c47feba144af09c989e5/Modules/itertoolsmodule.c#L965 https://github.com/python/cpython/blob/384621c42f9102e31ba2c... If you search for `list` in the CPython code, you'll find many examples of what you're asking about. Similarly, Pandas often makes a copy of a Series or DataFrame. It might be inefficient, but it keeps the API (more) simple.