TAMU ENGR 102 login.py (with hashing)

import sys
import getpass
import hashlib


def login(username: str = None, password: str = None) -> None:
    if not username:
        username = input('username: ')
    if not password:
        password = getpass.getpass('password: ')
    if authenticate(username, password):
        print('ACCESS GRANTED')
    else:
        print('ACCESS DENIED')


def authenticate(username: str, password: str) -> bool:
    try:
        stored_password_hash = get_password(username)
    except (FileNotFoundError, LookupError):
        return False
    h = hashlib.sha1()
    h.update(bytes(password,'utf-8'))
    password_hash = h.hexdigest()
    return stored_password_hash == password_hash


def get_password(username: str) -> str:
    # if user exists, return user's stored password
    # else raise Exception (file not found or user does not exist)
    username = username.lower()
    passwd = open('passwd')
    for line in passwd:
        # trim the newline
        line = line[:-1]
        uname, pword = line.split(':')
        if username == uname:
            return pword
    raise LookupError('user does not exist')


if __name__ == '__main__':
    argc = len(sys.argv)
    uname = sys.argv[1] if argc > 1 else None
    pword = sys.argv[2] if argc > 2 else None
    login(uname, pword)