How to handle command line arguments in Python
Sep 21, 2025 am 03:49 AM
The argparse module is the recommended way to handle command-line arguments in Python, providing robust parsing, type validation, help messages, and error handling; use sys.argv for simple cases requiring minimal setup.
Handling command line arguments in Python is straightforward and useful for making scripts more flexible. You can pass values directly from the terminal when running a script, which avoids hardcoding inputs. The most common and recommended way to do this is using the argparse module, part of Python’s standard library.
Using argparse for robust argument handling
The argparse module lets you define expected arguments, their types, help messages, and even handle optional flags. It automatically generates usage instructions and handles errors gracefully.
- Create an ArgumentParser object to configure your command-line interface
- Add arguments using add_argument(), specifying name, type, default value, and help text
- Call parse_args() to process the input and access the values
Example:
import argparse
parser = argparse.ArgumentParser(description="Process some numbers.")
parser.add_argument('number', type=int, help='a number to square')
parser.add_argument('--verbose', '-v', action='store_true', help='increase output verbosity')
args = parser.parse_args()
result = args.number ** 2
if args.verbose:
????print(f"The square of {args.number} is {result}")
else:
????print(result)
Run it via command line:
python script.py 5 -v
Handling optional and positional arguments
Positional arguments are required and given in order. Optional arguments start with -- or a short flag like -v. You can set defaults, make arguments required optionally, or allow multiple values.
- Use nargs='*' to accept zero or more values, or ' ' for one or more
- Set default= for fallback values when an optional argument isn’t provided
- Use choices=[...] to restrict input to specific values
Example with multiple inputs:
parser.add_argument('inputs', nargs=' ', type=float, help='numbers to sum')
Accessing raw arguments with sys.argv
If you need a lightweight approach without parsing logic, use sys.argv. It gives a list of all command-line inputs, where sys.argv[0] is the script name and the rest are arguments.
This method requires manual parsing and error handling but works for simple cases.
Example:
import sys
if len(sys.argv) > 1:
????print("Hello,", sys.argv[1])
else:
????print("No name provided")
Run: python script.py Alice
Basically just pick argparse for anything beyond basic input. It's clean, scalable, and user-friendly. For quick scripts, sys.argv gets the job done with minimal setup.
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