How to Sort Command-Line Arguments in Python

Build a beginner-friendly argparse CLI that sorts numbers or words passed as arguments, with an optional reverse flag.

Easy Python 3.9+ Aug 9, 2026 Automation & scripting 13 views 0 copies

argparse cli sorting beginner automation

Python code

20 lines

Python 3.9+

import argparse


def main():
    parser = argparse.ArgumentParser(description="Sort numbers or words from the command line.")
    parser.add_argument("items", nargs="+", help="Items to sort (numbers or words)")
    parser.add_argument("--reverse", "-r", action="store_true", help="Sort in descending order")
    args = parser.parse_args()

    try:
        values = [float(item) for item in args.items]
    except ValueError:
        values = args.items

    result = sorted(values, reverse=args.reverse)
    print("Sorted:", result)


if __name__ == "__main__":
    main()

Output

stdout

$ python sort_cli.py 5 3 8 1
Sorted: [1.0, 3.0, 5.0, 8.0]

$ python sort_cli.py banana apple cherry --reverse
Sorted: ['cherry', 'banana', 'apple']

How it works

The script uses argparse to parse command-line arguments, defining items as a variadic argument with nargs="+" to accept one or more values. It attempts to convert each item to a float using a list comprehension wrapped in a try/except; if any conversion fails, it falls back to treating them as strings. The sorted() function then sorts the values, and the --reverse flag (stored as a boolean by action="store_true") controls ascending or descending order. Finally, it prints the sorted result with a clear label.

Common mistakes

Forgetting to include `if __name__ == "__main__":` so the script runs when executed directly
Assuming items are always numbers; mixing numbers and words causes the fallback to string sorting
Not using `nargs="+"` so the CLI requires at least one value
Passing the `-r` flag as `--reverse=True` instead of just `--reverse`

Variations

Use `parser.add_argument('--key', default=None)` to sort by a custom key function
Add `parser.add_argument('--unique', action='store_true')` to remove duplicates with `set()` before sorting

Real-world use cases

Sorting filenames or log lines passed to a shell script for quick inspection in a pipeline.
Ranking numeric metrics like test scores or throughput values from a script invocation.
Preprocessing unsorted user input in an interactive automation tool before further processing.

How to Sort Command-Line Arguments in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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