def unflatten(dictionary):
    """Turn all keys with format {key}.{subkey} into nested dictionaries"""
    unflattened_dictionary = dict()
    for key, value in dictionary.items():
        parts = key.split('.')
        sub_dictionary = unflattened_dictionary
        for part in parts[:-1]:
            if part not in sub_dictionary:
                sub_dictionary[part] = dict()
            sub_dictionary = sub_dictionary[part]
        sub_dictionary[parts[-1]] = value
    return unflattened_dictionary
