Optparse module in Python

Optparse module makes easy to write command-line tools. It allows argument parsing in the python program.

• optparse make it easy to handle the command-line argument.
• It comes default with python.
• It allows dynamic data input to change the output
  

Code: Creating an OptionParser object.

Python3

import optparse
parser = optparse.OptionParser()

Defining options:

It should be added one at a time using the add_option(). Each Option instance represents a set of synonymous command-line option string.

Way to create an Option instance are:

       OptionParser.add_option(option)

       OptionParser.add_option(*opt_str, attr=value, ...)

 To define an option with only a short option string:

 parser.add_option("-f", attr=value, ....)

And to define an option with only a long option string:

parser.add_option("--foo", attr=value, ....)

Standard Option Actions: 

• “store”: store this option’s argument (default).
• “store_const”: store a constant value.
• “store_true”: store True.
• “store_false”: store False.
• “append”: append this option’s argument to a list.
• “append_const”: append a constant value to a list.

Standard Option Attributes:

• Option.action: (default: “store”)
• Option.type: (default: “string”)
• Option.dest: (default: derived from option strings)
• Option.default: The value to use for this option’s destination if the option is not seen on the command line.

Here’s an example of using optparse module in a simple script:

Python3

# import OptionParser class
# from optparse module.
from optparse import OptionParser

# create a OptionParser
# class object
parser = OptionParser()

# add options
parser.add_option("-f", "--file",
                  dest = "filename",
                  help = "write report to FILE",
                  metavar = "FILE")
parser.add_option("-q", "--quiet",
                  action = "store_false",
                  dest = "verbose", default = True,
                  help = "don't print status messages to stdout")

(options, args) = parser.parse_args()

With these few lines of code, users of your script can now do the “usual thing” on the command-line, for example:

<yourscript> --file=outfile -q

Lets, understand with an example:

Code: Writing python script for print table of n.

Python3

# import optparse module
import optparse

# define a function for
# table of n
def table(n, dest_cheak):
    for i in range(1,11):
        tab = i*n

        if dest_cheak:
            print(tab)

    return tab

# define a function for
# adding options
def Main():
    # create OptionParser object
    parser = optparse.OptionParser()

    # add options
    parser.add_option('-n', dest = 'num',
                      type = 'int',
                      help = 'specify the n''th table number to output')
    parser.add_option('-o', dest = 'out',
                      type = 'string',
                      help = 'specify an output file (Optional)')
    parser.add_option("-a", "--all",
                      action = "store_true",
                      dest = "print",
                      default = False,
                      help = "print all numbers up to N")

    (options, args) = parser.parse_args()
    if (options.num == None):
            print (parser.usage)
            exit(0)
    else:
            number = options.num

    # function calling
    result = table(number, options.print)

    print ("The " + str(number)+ "th table is " + str(result))

    if (options.out != None):
        # open a file in append mode
        f = open(options.out,"a")

        # write in the file
        f.write(str(result) + '\n')

# Driver code
if __name__ == '__main__':

    # function calling
    Main()

Output:

python file_name.py -n 4

python file_name.py -n 4 -o

file.txt created

python file_name.py -n 4 -a

For knowing more about this module click here.