function to unpack an inverted index with Python 3

unpack_inverted_index.py

import collections

def unpack_inverted_index(input):
    all_dict = {}
    for ind in input:
        for i in range(len(input[ind])):
            key = input[ind][i]
            all_dict[key] = ind
    sorted_dict = collections.OrderedDict(sorted(all_dict.items()))

    full_string = ""
    for item in sorted_dict.values():
        full_string += item + " "
    return full_string
  
#example: 
test_input = {'Is': [0], 'this': [1, 14], 'the': [3, 16], 'easiest': [4, 17], 'way': [5, 30], 'to': [6, 31], 'unpack': [7], 'an': [8, 26], 'inverted': [9], 'index?': [10], 'I': [11], 'think': [12], 'that': [13], 'is': [15, 25], 'way,': [18], 'please': [19], 'let': [20], 'me': [21], 'know': [22], 'if': [23], 'there': [24], 'easier': [27], 'or': [28], 'better': [29], 'do': [32], 'this!': [34]}
output = unpack_inverted_index(test_input)
print(output)