Getting a warning for the second argument of random.shuffle

Question

I want to use random.shuffle to randomize a list of strings. Here is a minimal example code:

import random
L = ['a', 'b']
random.shuffle(L, 3.0)

However, my IDE complains about the second argument. It highlights 3.0 with the following warning message:

Expected type 'Optional[() -> float]', got 'float' instead

What is this warning supposed to mean?

Answer 1

From the docs for random.shuffle

random.shuffle(x[, random])

Shuffle the sequence x in place.

The optional argument random is a 0-argument function returning a random float in [0.0, 1.0); by default, this is the function random().

(added bold)