Table of Contents
回复内容:
Home Backend Development Python Tutorial 如何看待以及理解Python的这种尾递归优化?

如何看待以及理解Python的这种尾递归优化?

Jun 06, 2016 pm 04:23 PM
decorator python

Python之父曾经明确表示Python将不会支持尾递归优化。但是最近查资料的时候发现了一种奇特的用decorator来进行尾递归优化的方法

Tail Call Optimization Decorator « Python recipes « ActiveState Code
Python与尾递归

首先这个是真正的尾递归优化么?其次如何理解这段代码它到底做了哪些事?

回复内容:

TCO,tail-call optimization,其实有多种解读方式。

最常见的解读方式是:对于尾调用的函数调用,不要浪费栈空间,而要复用调用者的栈空间。这样的结果就是一长串尾调用不会爆栈,而没有TCO的话同样的调用就会爆栈。
从这个意义上说,题主贴的那个recipe确实达到了TCO的部分目的:
  • 通过stack introspection查看调用链上的调用者之中有没有自己
  • 有的话,通过抛异常来迫使栈回退(stack unwind)到之前的一个自己的frame
  • 在回退到的frame接住异常,拿出后来调用的参数,用新参数再次调用自己
这样就可以让尾递归不爆栈。但这样做性能是没保证的…而且对于完全没递归过的一般尾调用也不起作用。

一种对TCO的常见误解是:由编译器或运行时系统把尾调用/尾递归实现得很快。这不是TCO真正要强调的事情——不爆栈才是最重要的。也就是说其实重点不在“优化”,而在于“尾调用不爆栈”这个语义保证。
“proper tail-call”的叫法远比“tail-call optimization”来得合适。

因而像题主说的那种做法,可以算部分TCO,但算不上“性能优化”意义上的优化。 突破人为设定的1000条限制,跟一般意义上的尾递归优化是有区别的。
Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

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

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

PHP and Python: Different Paradigms Explained PHP and Python: Different Paradigms Explained Apr 18, 2025 am 12:26 AM

PHP is mainly procedural programming, but also supports object-oriented programming (OOP); Python supports a variety of paradigms, including OOP, functional and procedural programming. PHP is suitable for web development, and Python is suitable for a variety of applications such as data analysis and machine learning.

Choosing Between PHP and Python: A Guide Choosing Between PHP and Python: A Guide Apr 18, 2025 am 12:24 AM

PHP is suitable for web development and rapid prototyping, and Python is suitable for data science and machine learning. 1.PHP is used for dynamic web development, with simple syntax and suitable for rapid development. 2. Python has concise syntax, is suitable for multiple fields, and has a strong library ecosystem.

Can visual studio code be used in python Can visual studio code be used in python Apr 15, 2025 pm 08:18 PM

VS Code can be used to write Python and provides many features that make it an ideal tool for developing Python applications. It allows users to: install Python extensions to get functions such as code completion, syntax highlighting, and debugging. Use the debugger to track code step by step, find and fix errors. Integrate Git for version control. Use code formatting tools to maintain code consistency. Use the Linting tool to spot potential problems ahead of time.

Can vs code run in Windows 8 Can vs code run in Windows 8 Apr 15, 2025 pm 07:24 PM

VS Code can run on Windows 8, but the experience may not be great. First make sure the system has been updated to the latest patch, then download the VS Code installation package that matches the system architecture and install it as prompted. After installation, be aware that some extensions may be incompatible with Windows 8 and need to look for alternative extensions or use newer Windows systems in a virtual machine. Install the necessary extensions to check whether they work properly. Although VS Code is feasible on Windows 8, it is recommended to upgrade to a newer Windows system for a better development experience and security.

Is the vscode extension malicious? Is the vscode extension malicious? Apr 15, 2025 pm 07:57 PM

VS Code extensions pose malicious risks, such as hiding malicious code, exploiting vulnerabilities, and masturbating as legitimate extensions. Methods to identify malicious extensions include: checking publishers, reading comments, checking code, and installing with caution. Security measures also include: security awareness, good habits, regular updates and antivirus software.

Python vs. JavaScript: The Learning Curve and Ease of Use Python vs. JavaScript: The Learning Curve and Ease of Use Apr 16, 2025 am 12:12 AM

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

PHP and Python: A Deep Dive into Their History PHP and Python: A Deep Dive into Their History Apr 18, 2025 am 12:25 AM

PHP originated in 1994 and was developed by RasmusLerdorf. It was originally used to track website visitors and gradually evolved into a server-side scripting language and was widely used in web development. Python was developed by Guidovan Rossum in the late 1980s and was first released in 1991. It emphasizes code readability and simplicity, and is suitable for scientific computing, data analysis and other fields.

How to run programs in terminal vscode How to run programs in terminal vscode Apr 15, 2025 pm 06:42 PM

In VS Code, you can run the program in the terminal through the following steps: Prepare the code and open the integrated terminal to ensure that the code directory is consistent with the terminal working directory. Select the run command according to the programming language (such as Python's python your_file_name.py) to check whether it runs successfully and resolve errors. Use the debugger to improve debugging efficiency.

See all articles