Error caused by print inside a list comprehension

[dilsonlira]

Bug Report

A function whose signature says it doesn't return anything (and it actually doesn't) gets a Mypy error: "print" does not return a value.

To Reproduce

A simplistic example:

# script1.py

def print_items_of_a_list(a: list) -> None:
    [print(item) for item in a]

Expected Behavior

Since the signature says it returns None and it actually returns None, this code is not supposed to cause an error.

Actual Behavior

script1.py:4: error: "print" does not return a value

Your Environment

• Mypy version used: 0.812
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): default
• Python version used: 3.6.0
• Operating system and version: macOS 11.3.1

[hauntsaninja]

Returning None and not returning is indistinguishable in Python. Most of the time this is a mistake / your code is not idiomatic / users have generally found this and similar warnings to be useful. I suggest type ignoring / ignoring the error code func-returns-value