第一个 Python argparse 位置参数只能是 str 类型吗？

Question

Am I right in the assumption that the first mandatory, positional argument added to argparse.ArgumentParser() instance can only be of type str ?

When I set it to float (or int ) and run the script in a shell, I get an invalid float value error. I doesn't matter whether I really pass in a float or even call -h for help, which should skip the parameter input and jump straight to the help section.

import argparse

parser = argparse.ArgumentParser(
    prog="add-expense"
)

parser.add_argument(
    "Amount",
    type=float
)

args = parser.parse_args()

When I place another parser.add_argument() of default type str before it, everything works fine.

Answer 1

With an added

print(args)

your script runs fine:

1013:~/mypy$ python3 stack69887099.py -h
usage: add-expense [-h] Amount

positional arguments:
  Amount

optional arguments:
  -h, --help  show this help message and exit
1013:~/mypy$ python3 stack69887099.py 1.232
Namespace(Amount=1.232)
1013:~/mypy$ python3 stack69887099.py test
usage: add-expense [-h] Amount
add-expense: error: argument Amount: invalid float value: 'test'