Solution: add numbers

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examples/regex/grades3.py

import re
import sys


def add_grades(filename):
    grades = {}
    with open(filename) as fh:
        for line in fh:
            if re.search(r'^\s*(#.*)?$', line):
                continue
            match = re.search(r'^\s*(\w+)\s*:\s*(\d+)\s*$', line)
            if match:
                name = match.group(1)
                value = int(match.group(2))
            else:
                raise Exception(f"Invalid row: '{line}'")
            if name not in grades:
                grades[name] = 0
            grades[name] += value
        for name in sorted(grades.keys(), key=lambda name: grades[name], reverse=True):
            print(f"{name:6}:{grades[name]:-3}")

if __name__ == '__main__':
    if len(sys.argv) != 2:
        exit(f"Usage: {sys.argv[0]} FILENAME")
    filename = sys.argv[1]
    add_grades(filename)