Have function reject bad argument when argument is called by another function?

[gontajones]

Please, use the same thread for same issues.

Check this implementation:

x = {"F": "Fluorine", "Cl": "Chlorine"}
y = {"O": "Oxygen"}


def hal(target_dict, key):
    try:
        # This will raise KeyError if not found
        print(target_dict[key])
    except KeyError:
        print(f'{key}: KeyError')


def acc(target_dict, key):
    try:
        # This will raise KeyError if not found
        print(target_dict[key])
    except KeyError:
        print(f'{key}: KeyError')


def is_halogen_bond(halogen, acceptor):
    hal(x, halogen)
    acc(y, acceptor)


user_key1 = input('Enter key 1: ')
user_key2 = input('Enter key 2: ')

while user_key1 != 'exit' and user_key2 != 'exit':
    is_halogen_bond(user_key1, user_key2)
    user_key1 = input('Enter key 1: ')
    user_key2 = input('Enter key 2: ')