python parser read_file() AttributeError: 'NoneType' object has no attribute 'infile'

Question

%%writefile testcipher.py
import argparse
def parse_command_line():
    parser=argparse.ArgumentParser()
    parser.add_argument("infile",type=argparse.FileType('r'),help="show this help message and exit")
    args=parser.parse_args()

def read_file(file_path):
    with open(file_path,"r") as f:
        message=f.read()
    return message
args = parse_command_line()
read_file(args.infile)

----------

%%bash

python3 testcipher.py plain_message.txt


----------

Traceback (most recent call last):
  File "testcipher.py", line 13, in <module>
    read_file(args.infile)
AttributeError: 'NoneType' object has no attribute 'infile'

I tried to read file with parser argument, somehow it didnt work..help please..

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Answer 1

(1) You need return 'args' in your parse_command_line() function.

(2) Your add_argment function lead to open file directly using your argument as file name.

%%writefile testcipher.py

import argparse
def parse_command_line():
    parser=argparse.ArgumentParser()
    parser.add_argument("infile",type=str,help="show this help message and exit")
    args=parser.parse_args()
    return args

def read_file(file_name):
    __file = open(file_name)
    message=__file.read()
    return message

args = parse_command_line()
message = read_file(args.infile)
print (message)

----------

%%bash

python3 testcipher.py plain_message.txt


----------

Answer 2

parse_command_line must return args object. Actually your parsing function returns None.

And of course None hasn't any attribute whatever it's name.