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

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. 

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.