reverse a csv file into new _reversed file (by keeping the header row) in python

reverse_csv.py

"""
This script reads a CSV file, reverses the order of its rows (except for the header), 
and writes the reversed content to a new CSV file '<input_csv>_reversed'.
"""

from pathlib import Path
import sys


def app():
    """
    Main application function.
    Checks for correct usage and valid CSV file input.
    """
    if len(sys.argv) != 2:
        print("Usage: python reverse.py <input_csv>")
        sys.exit(1)
    elif not sys.argv[1].endswith(".csv"):
        print("Please provide a valid CSV file.")
        sys.exit(1)
    else:
        csv_file = Path(sys.argv[1])
        read_reverse_write(csv_file)
    print(f"Reversed CSV file: {csv_name}_reversed{csv_ext}")


def read_reverse_write(csv_file: Path) -> None:
    """
    Reads the input CSV file, reverses its rows (except for the header),
    and writes the reversed content to a new CSV file called <filename>_reversed.
    
    Args:
        csv_file (Path): Path to the input CSV file.
    """
    csv_name, csv_ext = csv_file.stem, csv_file.suffix
    with open(csv_file, mode="r") as csv, open(f"{csv_name}_reversed{csv_ext}", mode="w") as out:
        lines = csv.readlines()
        for l in reverse_csv(lines):
            out.write(l)


def reverse_csv(csv_file: list[str]) -> list[str]:
    """
    Reverses the order of rows in the CSV file, keeping the header row in place.
    
    Args:
        csv_file (list[str]): List of rows from the CSV file.
    
    Returns:
        list[str]: List of rows with the order reversed, except for the header.
    """
    return [csv_file[0]] + csv_file[1:][::-1]


if __name__ == "__main__":
    app()