An argparse nargs problem

[dineshbvadhia]

Running mypy on the test_argparse.py program below generates the error:

> mypy test_argparse.py
test_argparse.py:12: error: Incompatible types in assignment (expression has type "str", variable has type "list[int]")  [assignment]

test_argparse.py

import argparse, sys
print(sys.argv)
# ['test_argparse.py', '--arg', '128', '64']
parser = argparse.ArgumentParser()
parser.add_argument('--arg', nargs='+', type=int)
arguments = parser.parse_args()
print(arguments)
# Namespace(arg=[128, 64])
d: dict[str, str] = vars(arguments)
v: list[int] = d['arg']             # L12
print(type(v), v)
# <class 'list'> [128, 64]

What is the problem and the correct type for v ?

[srittau]

d: dict[str, str] = vars(arguments)
v: list[int] = d['arg']             # L12

In line 11 (first line above) you are claiming that the dict returned by vars(arguments) has str values. And then in line 12 you try to assign one of those (supposedly) str values to a list[int]. You should change line 11 to either of those:

d = vars(arguments)
d: dict[str, Any] = vars(arguments)  # the annotation is redundant, but you might prefer explicit annotations

[dineshbvadhia]

Ah, that worked. Thank-you :)