Argparse error when inputting values

[tqader]

I'm trying to resolve the errors in this code. We are trying to use argparse, and I get to num_nums = len(args.n) and I get errors. The error gets generated when reading the next line and reads as:

ERROR CODE

Error:
print("Adding %d numbers." % num_nums)
TypeError: %d format: a number is required, not NoneType

I can't figure out what is failing with the %d argument that is being passed.
I am looking for assistance with the code to get it to a working state. Full code is:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument("-n", help="Number to add")
parser.add_argument("--indent", help="Indent output")

args = parser.parse_args()

num_nums = (args.n)
print("Adding %d numbers." % num_nums)
sum = 0
for n in range(0, num_nums):
    sum = sum + args.n[n]

if (args.i):
    print("\tSum = %d" % sum)
else:
    print("Sum = %d" % sum)

[bowlofred]

First, put your code inside python tags so it is easily readable (and so indentation can be seen).

Second, how are you running it? Are you giving an argument to -n? When I do I get a str error instead of a NoneType error.

You haven't told argparse that -n is required, so it will let you run without the argument. Also, the default is to read the argument as a string. So num_nums is a string and the print won't work when you ask it to format a string with %d.

You can modify the add_argument to resolve both. Something like

parser.add_argument("-n", type=int, required=True, help="Number to add")

[buran]

as a side note, you are using old-style string formatting, there is str.format() method and in 3.6+ - f-strings. better use f-strings.
also sum is built-in function. don't use it as name/variable.