I'm experimenting with argparse, the program works, but default values don't work. Here's my code:
'''This simple program helps you in understanding how to feed the user input from command line and to show help on passing invalid argument.'''
import argparse
import sys
def calc(args):
#Enable variables within the function to take on values from 'args' object.
operation = args.operation
x = args.x
y = args.y
if (operation == "add"):
return x + y
elif (operation == "sub"):
return x - y
parser = argparse.ArgumentParser(description="This is a summing program") #parser is an object of the class Argument Parser.
parser.add_argument("x", type=float, default=1.0, help="What is the first number?") #add_argument is a method of the class ArgumentParser.
parser.add_argument("y", type=float, default=1.0, help='What is the second number?')
parser.add_argument("operation", type=str, default="add", help='What operation? Can choose add, sub, mul, or div')
args = parser.parse_args()
print(str(calc(args)))
This simple program work, however attempting to call it without values returns the following error:
usage: cmdline.py [-h] x y operation
cmdline.py: error: the following arguments are required: x, y, operation
Where am I going wrong?
You are missing nargs='?'
. The following works:
import argparse
import sys
def calc(args):
#Enable variables within the function to take on values from 'args' object.
operation = args.operation
x = args.x
y = args.y
if (operation == "add"):
return x + y
elif (operation == "sub"):
return x - y
parser = argparse.ArgumentParser(description="This is a summing program") #parser is an object of the class Argument Parser.
parser.add_argument("x", nargs='?', type=float, default=1.0, help="What is the first number?") #add_argument is a method of the class ArgumentParser.
parser.add_argument("y", nargs='?', type=float, default=1.0, help='What is the second number?')
parser.add_argument("operation", nargs='?', type=str, default="add", help='What operation? Can choose add, sub, mul, or div')
args = parser.parse_args()
print(str(calc(args)))
Change these lines to indicate that you want named, optional command-line arguments (so "-x"
not "x"
):
parser.add_argument("-x", type=float, default=1.0, help="What is the first number?") #add_argument is a method of the class ArgumentParser.
parser.add_argument("-y", type=float, default=1.0, help='What is the second number?')
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