Removing spaces from dictionaries key-value pairs

Question

So this is my code for a program adding dicts together.

from collections import Counter
from itertools import chain

def add_sparse_vectors(lst1,lst2):
    dest = dict(Counter(lst1)+Counter(lst2))
    return dest

This is my current output:

>>> v1 = {0:1, 1:3, 2:1}
>>> v2 = {0:1}
>>> add_sparse_vectors(v1, v2)
{0: 2, 1: 3, 2: 1}

Problem is that my assignment asks for this output specifically:

>>> v1 = {0:1, 1:3, 2:1}
>>> v2 = {0:1}
>>> add_sparse_vectors(v1, v2)
{0:2, 1:3, 2:1}
#Note the lack of spaces between the colon and the value in each pair.

Does anyone have a solution for removing this specific space from the key-value pairs in the output? Any help is appreciated.

Answer 1

If you really want to get rid of the spaces, you don't need to implement a custom dict class, like @zondo suggested. The assignment only requires the representation to have no spaces. If add_sparse_vectors returns a string instead of a dictionary, you don't need to change dict 's behavior.

Although I don't think this is particularly elegant, it does get rid of the spaces.

def add_sparse_vectors(v1, v2):
    combined_dict = dict(Counter(lst1)+Counter(lst2))
    key_val_pairs = [str(k)+":"+str(v) for k,v in combined_dict.items()]
    output = "{" + ", ".join(key_val_pairs) + "}"
    return output

Answer 2

you can write your own print function for dictionaries:

def print_dict(d):
    print('{'+', '.join('{}:{}'.format(k, v) for k, v in d.items())+'}')

This does what your exercise asks for, but actually I think that they should not care about having some whitespaces more or less as long as the task is solved correctly...