Passing integer lists to python

Question

I want to pass 2 lists of integers as input to a python program.

For e.g, (from command line)

python test.py --a 1 2 3 4 5 -b 1 2  

Answer 1

argparse supports nargs parameter, which tells you how many parameters it eats. When nargs="+" it accepts one or more parameters, so you can pass -b 1 2 3 4 and it will be assigned as a list to b argument

# args.py
import argparse

p = argparse.ArgumentParser()

# accept two lists of arguments
# like -a 1 2 3 4 -b 1 2 3
p.add_argument('-a', nargs="+", type=int)
p.add_argument('-b', nargs="+", type=int)
args = p.parse_args()

# check if input is valid
set_a = set(args.a)
set_b = set(args.b)

# check if "a" is in proper range.
if len(set_a - set(range(1, 51))) > 0: # can use also min(a)>=1 and max(a)<=50
    raise Exception("set a not in range [1,50]")

# check if "b" is in "a"
if len(set_b - set_a) > 0:
    raise Exception("set b not entirely in set a")

# you could even skip len(...) and leave just operations on sets
# ...

So you can run:

$ python arg.py  -a 1 2 3 4 -b 2 20
Exception: set b not entirely in set a

$ python arg.py  -a 1 2 3 4 60 -b 2
Exception: set a not in range [1,50]

And this is valid:

$ python arg.py  -a 1 2 3 4 -b 2 3