Keys in dictionary python are mutable or immutable Careful not to add mutable values that could themselves be modified. May 28, 2022 · Python dictionary keys must always be immutable, which means you can not update the dictionary key in runtime. Common Immutable and Hashable Types: Well, the question is in the title: how do I define a python dictionary with immutable keys but mutable values? I came up with this (in python 2. Dec 10, 2017 · 6 I'm new to python and am just learning about immutable and mutable objects (I've never came across this before with my limited coding experience in MATLAB and C#). x): class FixedDict(dict): """ A dictionary 2 days ago · Why must dictionary keys be immutable? Why doesn’t list. This ensures the key's hash value remains constant, allowing efficient data retrieval. Understanding this concept is crucial for writing efficient and bug - free Python code, as it impacts how data is stored Use immutable keys only: Ensure dictionary keys are immutable types (strings, numbers, tuples of immutables) to maintain dictionary integrity. Be cautious with shared references: When dictionaries contain nested mutable objects (lists, other dictionaries), shallow copies do not duplicate these nested objects. It is not disallowed to create a mutable type that is hashable, but it might not behave as Sep 19, 2022 · To understand why dictionary keys must be immutable. Mutable and Immutable Objects in Python Let us see what are Python's Mutable vs Immutable Types in Python. Immutable data structures cannot be changed after they are created. A key represents what you want to search, and the value is the information associated with that key. The hash table implementation of dictionaries uses a hash value calculated from the key value to find the key. Feb 11, 2017 · An object kan be a key in a dictionary if it is hashable. Immutable even mean? Jun 13, 2012 · It's not hashable so you can't use it as a dictionary key (and it's "final", so you can't subclass it to override __hash__), but it's good enough if you want an immutable mapping to prevent accidental modification of a global value (like a class default attribute). Jan 26, 2025 · In this tutorial, you'll learn how Python mutable and immutable data types work internally and how you can take advantage of mutability or immutability to power your code. What Does Mutable vs. Oct 10, 2024 · In Python, dictionary keys must be immutable and hashable. Here is the definition of hashable from the documentation: Since object provides a default implementation of __hash__, __eq__ and __cmp__ this means that anything deriving from object is hashable unless it is explicitly defined not to be hashable. Limitations of Dictionary Keys 1. They are unordered collections of key - value pairs, where each key must be unique. Introduction to Python Dictionaries A dictionary in Python is a built-in data structure used to store data in the form of key–value pairs. Let us related it to hash table. However, there are certain limitations and considerations to keep in mind when working with dictionary keys in Python 3. But the Questions is Why? Jun 30, 2025 · In Python, data types can be classified into two main categories: mutable and immutable. What Does It Mean for Dictionaries to Be Mutable? Being mutable means that the state of the dictionary can change over time. 7) • Dynamically resizable • Based on hash Feb 8, 2025 · In Python, data structures are either mutable or immutable — but what does this really mean? Why does it matter? In this article, I will break down the difference, touch on how memory management works, and why immutable objects are crucial for thread safety and dictionary keys. On an abstract level, it consists of a key with an associated value. This means that you can modify the contents of a dictionary after it has been created. 1. Immutable Objects in Python Immutable Objects are of in-built datatypes like int, float, bool, string, Unicode, and tuple. A fundamental question that often arises is whether dictionary values can be mutable or immutable. You can add, update or remove key-value pairs in a dictionary which makes it a flexible and dynamic data structure. Python provides immutable alternatives to lists, sets and dictionaries. It is similar in spirit to List, Set, and Tuples. Dictionaries are: • Mutable • Unordered (conceptually; Python preserves insertion order as of 3. Understanding whether a data type is mutable or immutable is crucial as it affects how data is stored, modified, and passed around in a program. However, it is not indexed by a sequence of numbers but indexed based on keys and can be understood as associative arrays. I wanted to know why, if dicts in python are mutable, does editing a dict contained in a second dict not change the second dict? Jun 25, 2020 · Dictionary is a built-in Python Data Structure that is mutable. Uniqueness: As mentioned earlier, dictionary keys must be unique. A great practical application for dictionaries is memoization. If let's say the key was a mutable object, its value could change, and thus its hash could also change. We use dictionaries when we want to be able to quickly access additional data associated with a particular key. 5 days ago · In Python, dictionaries are one of the most powerful and widely used data structures. Let’s say you want to save Jul 11, 2025 · However, its state can be changed if it is a mutable object. In Python, the Dictionary represents the implementation of a hash-table. Feb 29, 2024 · Keys can be of any immutable type, such as numbers, strings, or tuples. Dictionaries themselves are mutable, but, dictionary keys can only be immutable types. Lists, sets and dictionaries are mutable, meaning we can add, update, or delete their elements. Jul 23, 2025 · In Python, dictionaries are mutable. We'll cover the fundamental concepts, usage methods, common Dictionaries Dictionaries are a useful type that allow us to store our data in key, value pairs. What are Keys? As May 28, 2024 · Mutable vs Immutable Mutable data structures can be changed after creation. A hashable object has a hash value that doesn't change during its lifetime and can be compared to other objects. In this blog post, we will focus on Python dictionaries and explore whether they are mutable. immutable objects, and key differences between Python 2 and 3 in handling these concepts. sort () return the sorted list? How do you specify and enforce an interface spec in Python? Why is there no goto? Why can’t raw strings (r-strings) end with a backslash? Why doesn’t Python have a “with” statement for attribute assignments? Why don’t generators support the with . You can perform several Nov 2, 2025 · In this blog, we’ll demystify mutability: how to check if an object is mutable, why dictionary keys have strict rules around mutability, how copying works differently for mutable vs. xjxwt zizm ldnhg qtzj wbhpzz xfzctubr ngsht juyz jnpyelv unsyussk qjxlb pmqd xwto joier mxp