import hashlib

def is_password_valid(uname, pw, prehashed=False):
    if prehashed:
        password_arg = pw
    else:
        hasher = hashlib.sha1()
        hasher.update(pw.encode())
        password_arg = hasher.hexdigest()

    user = get_user(uname)
    if user and user.password == password_arg:
        return True
    return False