running the python script in command line does not print any output

Question

I want to make a script in python and then run it from the command line. The script is called test.py and the command to run it is:

python3 test.py John Jackson

Here is the expected output:

John Jackson

And here is the python script I made:

class person:

    def __init__(self, first, last):
        self.firstname = first
        self.lastname = last

    def get_first(self):
        return self.firstname

    def get_last(self):
        return self.lastname

import argparse

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('first')
    parser.add_argument('last')
    args = parser.parse_args()
    c1 = person(args.first, args.last)
    print(c1)

But the problem is when I run the script from the command line using the mentioned command, it returns nothing. Do you know how to fix it and get the expected output?

Python does not automatically run a function called `main`. Some other languages may do that, but not Python. — hpaulj, May 18 '19 at 16:10

Gino Mempin · Answer 1 · 2019-05-18T13:29:22.237

5

You defined your main() function but did not call it.

Add this at the end of your script:

if __name__ == "__main__":
    main()

See What does if __name__ == “__main__”: do?.

Then, c1 is the person instance, which would print:

$ python3 test.py John Jackson
<__main__.person object at 0x104907ef0>

You need to call get_first() and get_last() to get the correct output:

print(c1.get_first(), c1.get_last())

edited May 18 '19 at 13:29

answered May 18 '19 at 12:24

Gino Mempin

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Akhil Batra · Accepted Answer · 2020-01-28T18:53:20.913

I am not sure if you are calling your main function while running the script.

Add

if __name__ == "__main__":
    main()

And override __str__ function of the person class to print first name and last name while passing class as argument to print.

def __str__(self):
    return self.firstname + ' ' + self.lastname

The whole code goes like this

import argparse

class person:

    def __init__(self, first, last):
        self.firstname = first
        self.lastname = last

    def get_first(self):
        return self.firstname

    def get_last(self):
        return self.lastname

    def __str__(self):
        return self.firstname + ' ' + self.lastname

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('first')
    parser.add_argument('last')
    args = parser.parse_args()
    c1 = person(args.first, args.last)
    print(c1)

if __name__ == '__main__':
    main()

LogicalBranch · Answer 3 · 2019-05-18T12:33:09.217

Your script is unnecessarily complex, a much (much) simpler way to achieve this is to use the argv property of the sys module then separate the (string) argument using split, like this:

import sys

name = sys.argv[1].split(" ")

if len(name) != 2:
  raise ValueError("Invalid first and last name, try using \"John Jackson\" instead.")

[first_name, last_name] = name
print(first_name, last_name)

You don't even need to raise an error:

import sys

name = sys.argv[1].split(" ")

if len(name) == 2:
  [first_name, last_name] = name
  print(first_name, last_name)

Then when you run the script like this:

python3 filename.py "John Jackson"

You should get the following output:

John Jackson

Good luck.

running the python script in command line does not print any output

3 Answers3