Why Is Python 3 Dictionary Key Ordering Non-Deterministic?
Non-Deterministic Ordering of Dictionary Keys in Python 3
In Python 2, the order of dictionary keys was consistent but not guaranteed. However, in Python 3, the ordering of dictionary keys obtained from functions like vars() appears non-deterministic.
Cause of the Non-Determinism
This change is attributed to a security fix implemented in Python 3.3. To prevent predictable hash values, a random seed is used in hash calculations. This randomization results in the unpredictable ordering of dictionary keys.
Preserving Ordering in Python 3.6 and Later
In Python 3.6, a new implementation of dictionaries was introduced that preserves the insertion order by default. From Python 3.7 onward, this behavior is guaranteed by the Python language specification.
Reversing the Non-Determinism
To disable hash randomization and revert to the previous behavior, set the PYTHONHASHSEED environment variable to 0. However, note that this is not advisable for security reasons.
Exception: Set Keys
Unlike dictionaries, sets in Python have always maintained insertion order, regardless of Python version.
Example: Consistent Dictionary Key Ordering
While dictionary keys are non-deterministic in Python 3.3, using sets to convert dictionary keys to strings preserves the order. For example:
<code class="python">set([str(i): i for i in range(10)].keys())</code>
This will consistently return the list ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'].
Additional Information
Refer to the object.__hash__() documentation for further details on hash randomization.
The above is the detailed content of Why Is Python 3 Dictionary Key Ordering Non-Deterministic?. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

Solution to permission issues when viewing Python version in Linux terminal When you try to view Python version in Linux terminal, enter python...

How to avoid being detected when using FiddlerEverywhere for man-in-the-middle readings When you use FiddlerEverywhere...

When using Python's pandas library, how to copy whole columns between two DataFrames with different structures is a common problem. Suppose we have two Dats...

How to teach computer novice programming basics within 10 hours? If you only have 10 hours to teach computer novice some programming knowledge, what would you choose to teach...

How does Uvicorn continuously listen for HTTP requests? Uvicorn is a lightweight web server based on ASGI. One of its core functions is to listen for HTTP requests and proceed...

Fastapi ...

Using python in Linux terminal...

Understanding the anti-crawling strategy of Investing.com Many people often try to crawl news data from Investing.com (https://cn.investing.com/news/latest-news)...
