command line arguments
passing command line arguments to a Python Script
When running a Python script at the command line (instead of inside IDLE, for example), you can pass it command line arguments.
As an example, this script takes a starting date and a number of weeks as arguments, and
then produces a calendar. The strings 2019-06-17 and 4 are passed to the script
as command line arguments.
python3 calmaker.py 2019-06-17 4
If you’ve set up your script with a shebang, you can just run it this way:
./calmaker.py 2019-06-17 4
Before reading the discussion below, you should already be familiar with:
- The “shebang” found at shebang
- The
if __name__=="__main__" block, explained here: main blocks
Basic use of argv
If you put this at the top of your Python file:
import sys
then anywhere in your Python file, you can access the list variable argv to get a list of the command line arguments to your script.
In the example
python3 calmaker.py 2019-06-17 4
The values of sys.argv woudl be:
sys.argv[0] == "calmaker.py"
sys.argv[1] == "2019-06-07"
sys.argv[2] == "4"
The number of arguments is available in len(sys.argv) which in this case would be 3. The name of the program is always
stored in sys.argv[0] and counts as one of the arguments.
Advanced use of command line arguments with argparse
In real world python coding, it is more common to use a library function called argparse to work with command line arguments.
The Offical Python website has documentation for argparse which can use accessed to learn more.