The main difference between a set and a dictionary in Python is that a set is an unordered collection of unique elements, while a dictionary is a collection of key-value pairs, where each key is unique.
A set is defined using curly braces or the built-in set() function, and it supports operations like union, intersection, difference, etc. It is mainly used to check for membership, remove duplicates, or perform set operations.
A dictionary is defined using curly braces or the built-in dict() function, and it is indexed by keys, which can be any hashable object. Each key maps to a value, and it supports operations like retrieving values by key, adding or removing key-value pairs, etc.
In summary, a set is used for mathematical set operations, while a dictionary is used for key-value mappings.