def reverse_dict_lookup(dictionary, value_to_find):
    """
    Looks up the key for the supplied value in dictionary dict.

    Args:
        dictionary: dictionary, the dictionary to do the reverse lookup
        value_to_find: the value to find in the dictionary
    
    Raises:
        KeyError if value does not exist in the dictionary
    """

    for key, value in dictionary.items():
        if value == value_to_find:
            return key
    else:
        raise KeyError("Could not find {} in map".format(value_to_find))