Command Line Arguments in Python

  • What are Command Line Arguments?

    • Command line arguments are values passed to a program when it is executed from the command line or terminal. They provide a way to customize the behavior of a program without modifying its source code.


  • How to Use Command Line Arguments in Python:

    • In Python, you can access command line arguments using the sys.argv list provided by the sys module. Each command line argument passed to the program is stored as a string in the sys.argv list.

    import sys

    # Access command line arguments
    arguments = sys.argv

    # Print command line arguments
    print("Command Line Arguments:", arguments)

  • Accessing Specific Command Line Arguments:

    • You can access specific command line arguments by indexing into the sys.argv list. Remember that the first element (sys.argv[0]) contains the name of the script itself, and subsequent elements contain the actual arguments.

    import sys

    # Access specific command line arguments
    script_name = sys.argv[0]
    first_argument = sys.argv[1]
    second_argument = sys.argv[2]

    # Print specific command line arguments
    print("Script Name:", script_name)
    print("First Argument:", first_argument)
    print("Second Argument:", second_argument)

  • Parsing Command Line Arguments :

    • To parse command line arguments more conveniently, you can use libraries like argparse or optparse. These libraries provide a structured way to define and handle command line options and arguments.

    import argparse

    # Create an ArgumentParser object
    parser = argparse.ArgumentParser(description='Process some integers.')

    # Add arguments
    parser.add_argument('integers', metavar='N', type=int, nargs='+',
    help='an integer for the accumulator')
    parser.add_argument('--sum', dest='accumulate', action='store_const',
    const=sum, default=max,
    help='sum the integers (default: find the max)')

    # Parse command line arguments
    args = parser.parse_args()

    # Print the result
    print(args.accumulate(args.integers))


  • Real-life examples of command-line arguments:

    • 1. Calculator Application:
    You are developing a command-line calculator application that performs basic arithmetic operations (addition, subtraction, multiplication, division) on two numbers provided as command-line arguments.

    Solution
    import sys

    # Check if correct number of arguments are provided
    if len(sys.argv) != 4:
    print("Usage: python calculator.py ")
    sys.exit(1)

    num1 = float(sys.argv[1])
    operation = sys.argv[2]
    num2 = float(sys.argv[3])

    if operation == '+':
    result = num1 + num2
    elif operation == '-':
    result = num1 - num2
    elif operation == '*':
    result = num1 * num2
    elif operation == '/':
    if num2 == 0:
    print("Error: Division by zero")
    sys.exit(1)
    result = num1 / num2
    else:
    print("Error: Invalid operation")
    sys.exit(1)

    print("Result:", result)

    2. File Converter:
    You want to create a command-line utility to convert text files from one format to another (e.g., from CSV to JSON). The input file and desired output format will be provided as command-line arguments.

    Solution
    import sys
    import csv
    import json

    # Check if correct number of arguments are provided
    if len(sys.argv) != 4:
    print("Usage: python converter.py input_file output_file format")
    sys.exit(1)

    input_file = sys.argv[1]
    output_file = sys.argv[2]
    output_format = sys.argv[3]

    if output_format not in ['csv', 'json']:
    print("Error: Invalid output format")
    sys.exit(1)

    if output_format == 'csv':
    # Convert JSON to CSV
    with open(input_file, 'r') as f:
    data = json.load(f)

    with open(output_file, 'w', newline='') as f:
    writer = csv.writer(f)
    writer.writerow(data[0].keys()) # Write header
    for row in data:
    writer.writerow(row.values())

    elif output_format == 'json':
    # Convert CSV to JSON
    with open(input_file, 'r') as f:
    reader = csv.DictReader(f)
    data = [row for row in reader]

    with open(output_file, 'w') as f:
    json.dump(data, f, indent=4)

    3. Password Generator:
    You want to create a command-line tool to generate random passwords of specified length. The desired length of the password will be provided as a command-line argument.

    Solution
    import sys
    import random
    import string

    # Check if correct number of arguments are provided
    if len(sys.argv) != 2:
    print("Usage: python password_generator.py < length>")
    sys.exit(1)

    length = int(sys.argv[1])

    password = ''.join(random.choices(string.ascii_letters + string.digits, k=length))
    print("Generated Password:", password)

    4. Data Analysis Tool:
    You are developing a command-line tool for basic data analysis tasks such as calculating the mean, median, and mode of a dataset provided as a command-line argument.

    Solution
    import sys
    import statistics

    # Check if correct number of arguments are provided
    if len(sys.argv) < 2:
    print("Usage: python data_analysis.py ...")
    sys.exit(1)

    data = [float(arg) for arg in sys.argv[1:]]

    mean = statistics.mean(data)
    median = statistics.median(data)
    mode = statistics.mode(data)

    print("Mean:", mean)
    print("Median:", median)
    print("Mode:", mode)

  • Summary:

    • Command line arguments provide a way to pass inputs to a Python program from the command line or terminal. By accessing the sys.argv list or using libraries like argparse or optparse, you can easily handle and parse command line arguments in your Python programs. This allows for greater flexibility and customization when running Python scripts from the command line.

    python All Chapters
    Introduction User Input If-Else Loops For loop While Loop Functions
    User Defined Functions String Functions Date Time Functions List Functions Arrays 2d Array Tuple Dictionary Oops Class Constructor Inheritance
    File handling CSV Command Line Arguments STACK & QUEUE Data Structures