How to write a python script that operates on a list of input files?

How to write a python script that operates on a list of input files?

I have a program that takes an input file:
python subprogram.py < input.txt > out.txt
If I have a number of input files, how can I write a single python program
runs on those inputs and produces a single output? I believe the program
should run like:
python program.py < input_1.txt input_2.txt > out.txt
And the program itself should look something like:
from subprogram import MyClass
import sys
if __name__ == '__main__':
myclass = MyClass()
myclass.run()