Define the class to read arguments

To use arguments passed by parameter in a Python script you can use the following library

from argparse import ArgumentParser
import sys

# ArgumentParser with a description of the application 
parser = ArgumentParser(description='%(prog)s is an ArgumentParser demo')

Example of required arguments

# Positional argument with description
parser.add_argument('file', help='help of file')

Example of optional arguments

# Positional argument. If it is parameterized, it requires an integer value
# (Https://docs.python.org/3/library/argparse.html#type)
parser.add_argument('value', help='help for opt3', type=int)

# Positional argument with three possible options, can be called with -f or -fruit 
# (Https://docs.python.org/3/library/argparse.html#choices) 
parser.add_argument('-f','--fruit', choices=['pears', 'apples', 'oranges']) 

# Optional argument with description. If parameter requires integer, default is 10 
parser.add_argument('-v', help='help for opt4', type=int, default=10)

# Optional argument. With ' action ' we value if the argument is parameterized 
# (Https://docs.python.org/3/library/argparse.html#action)
parser.add_argument('-op1', '--option1', help='help for opt5', action='store_true', default=False)

# Optional argument that requires two arguments
parser.add_argument('-op2', nargs=2)

# Optional argument that requires 1 to N arguments
parser.add_argument('-op3', nargs='+')

# Optional argument that requires 0 to N arguments
parser.add_argument('-op4', nargs='*')

Reading arguments in code

# Finally parse the arguments
args = parser.parse_args()

# Print parameter
print ('File:', args.file)
print ('Integer number:', args.value)
print ('Fruit choise:', args.fruit)
print ('Value choise:', args.v)
print ('Option 1:', args.option1)
print ('Option 2:', args.op2)
print ('Option 3:', args.op3)
print ('Option 4:', args.op4)

# get input data:
if args.file != None:
    print("\n\nInput file: " + args.file )
    inputfile = args.file
else:
    sys.stderr.write("Please, Specify a file!\n")
    sys.exit(2)

Running Python scripts with arguments

All the content described above is saved in a file called “prueba.py” and when executing it, it would give us the following output that shows the correct functioning.

> test.py file.txt 2

File: file. txt
Integer parsed number: 2
Select fruits: None
Select Value: 10
Option 1: False
Option 2: None
Option 3: None
Option 4: None

Input file: file.txt