Split string by N symbols in Python from the end of the string

I need to split the string from the end.
For example, I have

word = '3640000'

And it is easy to split it from the begin of the string using list generator and .join method:

word = ' '.join([word[i:i + 3] for i in range(0, len(word), 3)])

In this case I get result: ‘364 000 0’

but I need get: "3 640 000"

How can I solve this task?

I tried something like this, but it is not working for me if a word is not divisible by 3 without remainder

list1 = []
for i in range(len(word) - 1, -1, -3):
    print(word[i-2:i+1])
    list1.append(word[i-2:i+1])
list1.reverse()

>Solution :

It’s a bit hacky, we can use Python’s string formatting to do the grouping, then replace the separator (Python only allows "," and "_" as grouping characters).

>>> w = '3640000'
>>> f'{int(w):,d}'.replace(',', ' ')
'3 640 000'