Argument Parser in Python

Python argparse - Concise Notes

argparse is a Python library for parsing command-line arguments. It provides a simple interface to define, process, and handle arguments.

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Basic Usage

1. Setup

   import argparse
   parser = argparse.ArgumentParser(description="A simple script")
   

2. Adding Arguments

3. Positional Argument: Required, order matters

   parser.add_argument("filename", help="File to process")
   

4. Optional Argument: Starts with -- or -, order doesn’t matter.

   parser.add_argument("--verbose", action="store_true", help="Enable verbose output")
   parser.add_argument("-n", "--number", type=int, default=1, help="Number of iterations")
   

5. Parsing Arguments

args = parser.parse_args()
print(args.filename)      # Positional argument
print(args.verbose)       # True/False (store_true)
print(args.number)        # Integer value (default: 1)

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Key Argument Settings

1. Positional Arguments:
2. No special prefix.

3. Example: python script.py input.txt

4. Optional Arguments:

5. Use - or --.

6. Example: python script.py --verbose

7. Argument Types:

8. Specify with type (e.g., int, float, str).

9. Example:

   parser.add_argument("--value", type=float, help="A float value")
   

10. Default Values:

11. Use default.

12. Example:

    parser.add_argument("--name", default="User", help="Default name")
    

13. Boolean Flags:

14. Use action="store_true" or action="store_false".

15. Example:

    parser.add_argument("--debug", action="store_true", help="Enable debug mode")
    

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Example Usage

Script:

import argparse

parser = argparse.ArgumentParser(description="Demo script")
parser.add_argument("filename", help="Input file name")
parser.add_argument("-v", "--verbose", action="store_true", help="Enable verbosity")
parser.add_argument("-n", "--number", type=int, default=10, help="Number of items")
args = parser.parse_args()

print(f"Filename: {args.filename}")
print(f"Verbose: {args.verbose}")
print(f"Number: {args.number}")

Run:

python script.py file.txt --verbose -n 5

Output:

Filename: file.txt
Verbose: True
Number: 5

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Common Methods

1. parser.add_argument(): Define arguments.
2. parser.parse_args(): Parse command-line inputs.

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Tips

• Use help for clear CLI documentation.
• Default type is str if not specified.
• Boolean flags (store_true) are ideal for toggles.

For most cases, this basic usage suffices!