1

I'm learning to include command line parameters in my code. I've read the docs for argparse and I tried running this script from there.

#argparse_trial.py

import argparse

parser = argparse.ArgumentParser(description='Process some integers.')
parser.add_argument('integers', metavar='N', type=int, nargs='+',
                help='an integer for the accumulator')
parser.add_argument('--sum', dest='accumulate', action='store_const',
                const=sum, default=max,
                help='sum the integers (default: find the max)')

args = parser.parse_args()
print(args.accumulate(args.integers))

If I run

>python argparse_trial.py 1

in the command line, I get the expected result 1
But if I run

>argparse_trial.py 1

I get 

usage: arg_parse_trial.py [-h] [--sum] N [N ...]
argparse_trial.py: error: the following arguments are required: N

I checked and the only argument the code seems to receive in the second case is the filename itself, no matter how many arguments are given.
I'm on a Windows machine and python is in my path.

Why is the second case failing in this script? How can I get it to work?

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9
  • I don't know how to phrase this question properly, so feel free to make it better Commented Jun 9, 2016 at 5:02
  • I'm not sure how you are able to execute a python script without the python executable. At least on Windows. Commented Jun 9, 2016 at 5:04
  • Like I said, python is in my path Commented Jun 9, 2016 at 5:05
  • But you're not typing its name, so the system will not look for it. Commented Jun 9, 2016 at 5:06
  • Well, how come the file is executed then? I run all my .py files without adding python before them and they've all worked properly till now Commented Jun 9, 2016 at 5:08

4 Answers 4

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2

This is a guess, I cannot test right now, but I believe this is what is happening:

  1. you type the name of your python file.
  2. Windows fails to run the file as a program, so…
  3. Windows tries to open the file, using the associated program (kindof with using start).
  4. While doing so, it simply ignores other things on the line, and…
  5. …generates a basic command line for the python interpreter to use, featuring just the interpreter itself and the target file to open.

Think of what happens when you "run" a text document.

If the command line is not generated correctly, running this command should fix it (replace the path as appropriate):

ftype Python.File=C:\Path\to\python.exe "%1" %*

Notice the %* at the end. If it's amiss, arguments will be dropped.

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19 Comments

Thanks for the answer. But I run youtube-dl on a regular basis. I've never included python before it and it accepts a lot of command-line arguments
Can you check you python file association then? It should look like D:\Program Files\Python\python.exe "%1" %*. If the %* is missing, it could cause arguments to be dropped.
@GughanRavikumar> the settings that tell windows how to open a .py file.
yes, because these are all exe files and will work if you have path provided in the environment variable.
check C:/Python27/Scripts and see.
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2

I think the code is working fine. You can execute the program by just choosing the default program to be python.exe for python files.
In your case python.exe "1" %* as @spectras suggested, so it will be able take command line arguments.

Also provide the path environment variable.
Programs like pip,virtualenv and youtube-dl are all executable files and if have already set the environment variable, we use it anywhere.

How to choose default program on windows:
http://windows.microsoft.com/en-in/windows/change-default-programs#1TC=windows-7

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1 Comment

My default program is python.exe. It has to be python.exe "1" %*, thanks to @spectra. Just change that, I'll make yours the accepted answer
0

You can Use sys library included in python and use argv() function to perform various command argunment.

find this video tutorial intuitive to understand how to!

https://www.youtube.com/watch?v=rLG7Tz6db0w

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0

This is in addition to spectras' and Bhansa's answer.
For Windows 10 user's, setting advanced file associations is a bit complicated. You'll have to edit your registry files. Run regedit.
Go to HKEY_CURRENT_USER\SOFTWARE\Classes\py_auto_file\shell\open\command and change the value of Data from
"C:\Path\To\Python\python.exe" "1"
to
"C:\Path\To\Python\python.exe" "1" %*

This might be applicable to previous versions of Windows also.

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2 Comments

The configuration is FUBAR'd if .py files are using the automatically generated py_auto_file ProgId. Make sure that .py files are associated with Python.File. I would delete the py_auto_file entry and use Explorer's "open with" or the settings app to select the correct "Python" ProgId. If the command-line template is wrong, use regedit to modify Python.File in the user's HKCU (for an all-users installation, you can use cmd's assoc and ftype to modify the HKLM values). If Python 3 is installed, use the fully qualified path to the "py.exe" laucher (try where py.exe in cmd).
@eryksun I'm sorry, I didn't understand most of what you said. I've explained what I did to get it working on my system. Using explorer's open with you can't set advanced options, like %* So I had to edit the registry to get it working

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