CODEWITHSUNDEEP
pythonlist
CAD97
CAD97

Reputation: 1313

Overhead of list() on a list

In certain styles of python, everything is a generator, e.g. uses yield rather than constructing and returning a list. If you need to use it as a list, you can just call list(gen).

If I have a list already, what is the cost of calling list(my_list)?

Use: I have a variable that I know has an iterator and might be a list, but I need to use it as a list. Is it better/more pythonic to do my_list = list(my_list) or some other way of checking its list-ness?

If it matters I'm using Python 3.5.

Upvotes: 4

Views: 173

Answers (1)

khelwood
khelwood

Reputation: 59114

If you call list(x) you are certainly creating a new list, even if x is already a list. If you want to avoid it, you can use isinstance(x, list) to check if x is a list or not.

if not isinstance(x, list):
    x = list(x)

Upvotes: 5

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