How send parameters through a pipe in a python script using argparse?

Question

I have to create a python script that can be used with Linux pipes

I want to run an script where some parameters can be send with a pipe or in the same line

Some examples of the use of my script with the expected output:

echo "a" > list.txt
echo "b" >> list.txt

./run.py p1 p2   # ['p1', 'p2'] expected output
cat list.txt | ./run.py  # ['a', 'b'] expected output
cat list.txt | ./run.py p1 p2 # ['p1', 'p2', 'a', 'b'] expected output

I tried:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('args', nargs=argparse.REMAINDER)
args = parser.parse_args().args
print args

It works only with the parameters in the same line:

./run.py p1 p2  #['p1', 'p2'] OK
cat list.txt | ./run.py  # []  Not OK
cat list.txt | ./run.py p1 p2 # ['p1', 'p2'] expected output

Answer 1

A solution by using only argparse

import argparse
import sys

parser = argparse.ArgumentParser()
parser.add_argument('args', nargs=argparse.REMAINDER)
parser.add_argument('stdin', nargs='?', type=argparse.FileType('r'), default=sys.stdin)
args = parser.parse_args().args

if not sys.stdin.isatty():
    stdin = parser.parse_args().stdin.read().splitlines()
else:
    stdin = []

print(args + stdin)

nargs='?' makes stdin optional and sys.stdin.isatty() checks if sys.stdin is empty