python error 'dict' object has no attribute: 'add'

Question

I wrote this code to perform as a simple search engine in a list of strings like the example below:

mii(['hello world','hello','hello cat','hellolot of cats']) == {'hello': {0, 1, 2}, 'cat': {2}, 'of': {3}, 'world': {0}, 'cats': {3}, 'hellolot': {3}}

but I constantly get the error

'dict' object has no attribute 'add'

how can I fix it?

def mii(strlist):
    word={}
    index={}
    for str in strlist:
        for str2 in str.split():
            if str2 in word==False:
                word.add(str2)
                i={}
                for (n,m) in list(enumerate(strlist)):
                    k=m.split()
                    if str2 in k:
                        i.add(n)
                index.add(i)
    return { x:y for (x,y) in zip(word,index)}

Answer 1

In Python, when you initialize an object as word = {} you're creating a dict object and not a set object (which I assume is what you wanted). In order to create a set, use:

word = set()

You might have been confused by Python's Set Comprehension, e.g.:

myset = {e for e in [1, 2, 3, 1]}

which results in a set containing elements 1, 2 and 3. Similarly Dict Comprehension:

mydict = {k: v for k, v in [(1, 2)]}

results in a dictionary with key-value pair 1: 2.

Answer 2

x = [1, 2, 3] is a literal that creates a list (mutable array).
x = [] creates an empty list.

x = (1, 2, 3) is a literal that creates a tuple (constant list).
x = () creates an empty tuple.

x = {1, 2, 3} is a literal that creates a set.
x = {} confusingly creates an empty dictionary (hash array), NOT a set, because dictionaries were there first in python.

Use
x = set() to create an empty set.

Also note that
x = {"first": 1, "unordered": 2, "hash": 3} is a literal that creates a dictionary, just to mix things up.