All of your code should go into arithmetic_arranger.py and be called from main.py
main.py should be this:
# This entrypoint file to be used in development. Start by reading README.md
from pytest import main
from arithmetic_arranger import arithmetic_arranger
print(arithmetic_arranger(['3801 - 2', '123 + 49']))
# Run unit tests automatically
main(['-vv'])
And in your .replit change this line
run = “python arithmetic_arranger.py”
to this
run = “python main.py”
Then you will see some verbose errors indicating a problem with extra spaces