Adventures in Machine Learning

Unhashable Type Error in Python: Solutions and Prevention Tips

Unhashable Type with Sets in Python: An Informative Guide

Python is an object-oriented programming language known for its ease of use and readability. It is widely used in various fields, such as data science, web development, and automation.

One of the essential features of Python is its data structures, which include sets, dictionaries, and lists. These data structures are mutable, meaning that their contents can be changed.

However, sets and dictionaries have a unique requirement: the elements they contain must be hashable. Hashable vs.

Unhashable Objects

So what does it mean for an object to be hashable? Simply put, hashable objects are immutable, meaning that their contents cannot be changed.

Examples of hashable objects include strings, integers, and boolean values. These objects are hashable because they have a unique identifier, or hash value, which remains constant throughout the object’s lifetime.

On the other hand, unhashable objects are mutable, meaning that their contents can be changed. Examples of unhashable objects include lists, dictionaries, and sets.

These objects cannot be used as elements of sets or keys of dictionaries because they do not have a unique identifier. Causes of the Error: Unhashable Type with Sets in Python

The unhashable type error occurs when you attempt to use an unhashable object, like a set, as a key in a dictionary or as an element in another set.

This error occurs because sets are mutable objects, and their contents can be changed even after they are created. As a result, their hash values may change, making them unhashable.

Solution 1: Use Frozenset Instead

One solution to this error is to use a frozenset instead of a set. A frozenset is an immutable version of a set, which means that its elements cannot be changed.

Because frozensets are immutable, they have a unique identifier that remains constant throughout their lifetime, making them hashable. Here’s an example:

# Using a frozenset as a key in a dictionary

dictionary = {frozenset({1, 2}): ‘value’}

print(dictionary[frozenset({1, 2})]) # Output: ‘value’

Solution 2: Use Tuple Instead

Alternatively, you can use a tuple instead of a set.

Tuples are immutable, which means that their elements cannot be changed. They are also hashable, making them suitable for use as keys in dictionaries and elements in sets.

Here’s an example:

# Using a tuple as a key in a dictionary

dictionary = {(1, 2): ‘value’}

print(dictionary[(1, 2)]) # Output: ‘value’

Checking Object Type with Type() and isinstance()

Understanding the type of objects you are working with is critical to avoiding errors in your Python programs. You can use the type() function to get the type of an object.

For example:

# Using type() function

print(type(‘Hello world’)) # Output: . You can also use the isinstance() function to check if an object is an instance of a particular class or subclass.

For example:

class Animal:


class Cat(Animal):


cat = Cat()

# Using isinstance() function

print(isinstance(cat, Animal)) # Output: True

print(isinstance(cat, Cat)) # Output: True

Additional Resources

Python has a vast community, and there are several resources available to help you learn more about error handling and other Python concepts. Here are some additional resources for those interested:

– Official Python Documentation: The official Python documentation is a comprehensive resource for developers of all skill levels.

It includes detailed explanations of Python syntax, modules, and packages. – Python Reddit: The Python subreddit is a community of developers who share news, tutorials, and resources related to Python.

– Python Weekly: Python Weekly is a weekly newsletter that covers Python news, tutorials, and resources. – Python Crash Course: A book by Eric Matthes that teaches Python programming from scratch.


In this guide, we discussed the causes of the unhashable type error with sets in Python and provided two solutions to the problem. We also explained the differences between hashable and unhashable objects and how to use the type() and isinstance() functions in Python.

Finally, we provided additional resources for those interested in learning more about Python programming. In this informative article, we discussed the unhashable type error with sets in Python and the importance of understanding hashable vs.

unhashable objects. We provided two solutions to the problem, using frozensets or tuples instead of sets, and explained how to use the type() and isinstance() functions in Python.

It is vital to understand this error because it can lead to unexpected program behavior and slow down the development process. Remember to use immutable objects like tuples and frozensets instead of mutable ones like sets whenever possible, and check object types using type() and isinstance().

With this knowledge, you can write more robust and efficient Python programs.