Python mypy: float and int are incompatible types with numbers.Real

Question

I am new to Python's static typing module mypy. I am trying to append ints and floats to an array, which I typed statically to be Real. But mypy says that they are incompatible types with Real. I thought ints and floats are a subtype of Real?

from typing import List
from numbers import Real

data : List[Real] = []
with open(path, 'r') as file:
    for line in file:
        line = line.strip()
        if subject == 'time':
            data.append(float(line))
        else:
            data.append(int(line))

Error message:

graph.py:56: error: Argument 1 to "append" of "list" has incompatible type "float"; expected "Real"
graph.py:58: error: Argument 1 to "append" of "list" has incompatible type "int"; expected "Real"

Answer 1

As AChampion says you can just use float in place of numbers.Real. Pep 0484 (specifically here) basically says that in the context of type-checking the hierarchy complex > float > int is respected and that numbers.* doesn't need to be used.

This is a known 'issue' with mypy and was raised and discussed here. I haven't read the entire discussion but the tldr seems to be that Pep 0484 is enough to make this a low priority issue (and it hasn't been resolved in 5 years).

I will say that (as the issue discussion mentioned) it would be nice if mypy gave some indication of this as a known issue in it's error message, which it currently (mypy 0.991) doesn't.