Python getopt Module

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The getopt module in Python provides a way to parse command-line options and arguments. It is a simpler alternative to the more powerful argparse module, and it is similar in functionality to the C library's getopt() function.

Table of Contents

1. Introduction
2. Key Functions
   • getopt
3. Examples
   • Parsing Command-Line Options
   • Handling Both Short and Long Options
   • Using Default Values
4. Real-World Use Case
5. Conclusion
6. References

Introduction

The getopt module is used to parse command-line options and arguments. It provides a straightforward way to handle options and arguments, making it suitable for simple command-line scripts.

Key Functions

getopt

Parses command-line options and arguments.

import getopt
import sys

opts, args = getopt.getopt(sys.argv[1:], 'ho:v', ['help', 'output=', 'verbose'])

• sys.argv[1:]: The list of command-line arguments passed to the script, excluding the script name.
• 'ho:v': Short option definitions. Options that require an argument are followed by a colon (:).
• ['help', 'output=', 'verbose']: Long option definitions. Options that require an argument are followed by an equals sign (=).

Examples

Parsing Command-Line Options

import getopt
import sys

def main():
    try:
        opts, args = getopt.getopt(sys.argv[1:], 'ho:v', ['help', 'output=', 'verbose'])
    except getopt.GetoptError as err:
        print(err)
        sys.exit(2)
    
    output = None
    verbose = False
    
    for o, a in opts:
        if o in ('-h', '--help'):
            print('Usage: script.py -o <outputfile> -v')
            sys.exit()
        elif o in ('-o', '--output'):
            output = a
        elif o in ('-v', '--verbose'):
            verbose = True
        else:
            assert False, 'Unhandled option'
    
    print(f'Output: {output}')
    print(f'Verbose: {verbose}')

if __name__ == '__main__':
    main()

Command Line:

$ python script.py -o result.txt -v

Output:

Output: result.txt
Verbose: True

Handling Both Short and Long Options

import getopt
import sys

def main():
    try:
        opts, args = getopt.getopt(sys.argv[1:], 'hi:o:', ['help', 'input=', 'output='])
    except getopt.GetoptError as err:
        print(err)
        sys.exit(2)
    
    inputfile = None
    outputfile = None
    
    for o, a in opts:
        if o in ('-h', '--help'):
            print('Usage: script.py -i <inputfile> -o <outputfile>')
            sys.exit()
        elif o in ('-i', '--input'):
            inputfile = a
        elif o in ('-o', '--output'):
            outputfile = a
        else:
            assert False, 'Unhandled option'
    
    print(f'Input file: {inputfile}')
    print(f'Output file: {outputfile}')

if __name__ == '__main__':
    main()

Command Line:

$ python script.py -i input.txt --output=output.txt

Output:

Input file: input.txt
Output file: output.txt

Using Default Values

import getopt
import sys

def main():
    inputfile = 'default_input.txt'
    outputfile = 'default_output.txt'
    
    try:
        opts, args = getopt.getopt(sys.argv[1:], 'hi:o:', ['help', 'input=', 'output='])
    except getopt.GetoptError as err:
        print(err)
        sys.exit(2)
    
    for o, a in opts:
        if o in ('-h', '--help'):
            print('Usage: script.py -i <inputfile> -o <outputfile>')
            sys.exit()
        elif o in ('-i', '--input'):
            inputfile = a
        elif o in ('-o', '--output'):
            outputfile = a
        else:
            assert False, 'Unhandled option'
    
    print(f'Input file: {inputfile}')
    print(f'Output file: {outputfile}')

if __name__ == '__main__':
    main()

Command Line:

$ python script.py

Output:

Input file: default_input.txt
Output file: default_output.txt

Real-World Use Case

Batch Processing Script

import getopt
import sys

def process_files(inputfile, outputfile):
    print(f'Processing input file: {inputfile}')
    print(f'Saving results to: {outputfile}')

def main():
    inputfile = None
    outputfile = None
    
    try:
        opts, args = getopt.getopt(sys.argv[1:], 'hi:o:', ['help', 'input=', 'output='])
    except getopt.GetoptError as err:
        print(err)
        sys.exit(2)
    
    for o, a in opts:
        if o in ('-h', '--help'):
            print('Usage: script.py -i <inputfile> -o <outputfile>')
            sys.exit()
        elif o in ('-i', '--input'):
            inputfile = a
        elif o in ('-o', '--output'):
            outputfile = a
        else:
            assert False, 'Unhandled option'
    
    if inputfile and outputfile:
        process_files(inputfile, outputfile)
    else:
        print('Usage: script.py -i <inputfile> -o <outputfile>')
        sys.exit(2)

if __name__ == '__main__':
    main()

Command Line:

$ python script.py -i data.txt -o result.txt

Output:

Processing input file: data.txt
Saving results to: result.txt

Conclusion

The getopt module in Python provides a simple way to parse command-line options and arguments. It is useful for basic scripts and when you need to quickly add command-line argument parsing to a program. For more complex command-line interfaces, consider using the argparse module.

References

• Python getopt module documentation

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