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Understanding python.analysis.languageServerMode in Pylance

Pylance is a fast, feature-rich language support extension for Python in Visual Studio Code, powered by the Pyright static type checker. It provides advanced type checking, auto-completions, code navigation, and other language features to enhance your Python development experience.

One of Pylance's configurable settings is python.analysis.languageServerMode, which allows you to optimize Pylance's performance based on your development needs.

This guide explains what python.analysis.languageServerMode is, how it affects Pylance's functionality, and how you can customize it to suit your preferences.

What is python.analysis.languageServerMode?

The python.analysis.languageServerMode setting in Pylance offers predefined configurations to help users optimize Pylance's performance based on their development needs. It controls how many IntelliSense features Pylance provides, allowing you to choose between full language service functionality or a lightweight experience optimized for performance.

By adjusting this setting, you can strike a balance between the richness of features and the performance impact on your system.

Accepted Values

  • default (default value)
  • light

Descriptions

  • default: Provides a balanced experience with many useful features enabled by default. This mode ensures that Pylance delivers sufficient functionality for most users without overloading the system. Advanced features like full language analysis, indexing, and IntelliSense are enabled, allowing for a comprehensive development experience.

  • light: Designed for users seeking a lightweight, memory-efficient setup. This mode disables various features to make Pylance function more like a streamlined text editor. It is ideal for those who do not require the full breadth of IntelliSense capabilities and prefer Pylance to be as resource-friendly as possible.

Modifications to Default Settings

When you change the python.analysis.languageServerMode setting, Pylance automatically adjusts several other settings to match the selected mode. Below are the default values for each mode:

Setting default mode light mode
python.analysis.exclude [] ["**"]
python.analysis.useLibraryCodeForTypes true false
python.analysis.enablePytestSupport true false
python.analysis.indexing true false

  • python.analysis.exclude: Specifies paths to directories or files that Pylance should not include in the analysis. In light mode, it is set to ["**"], which means Pylance will exclude all files from workspace, enabling IntelliSense support for open files only.

  • python.analysis.useLibraryCodeForTypes: When set to true, Pylance parses the source code of libraries when type stubs are not available. In light mode, this is set to false, reducing memory usage.

  • python.analysis.enablePytestSupport: Enables Pytest-specific IntelliSense features. Disabled in light mode to reduce resource consumption.

  • python.analysis.indexing: Indexes installed third-party libraries and user files to improve features like auto-imports and symbol searches. Disabled in light mode for performance optimization.

These settings can be individually customized to override the defaults for each mode.

How to Change the Setting

  1. Open Settings: Click on the gear icon in the lower-left corner of Visual Studio Code and select Settings.
  2. Search for the Setting: Type python.analysis.languageServerMode in the search bar.
  3. Modify the Setting: Choose default or light from the dropdown menu.

Alternatively, you can edit your settings.json file directly:

  1. Open Settings (JSON): Open the command palette and type Preferences: Open Settings (JSON).
  2. Add or Modify the Setting: 
    "python.analysis.languageServerMode": "light"

When and Why to Use light Mode

  • Large Projects: Improves performance by analyzing only open files, reducing resource usage.
  • Limited Resources: Suitable for systems with low memory or CPU power.
  • Quick Edits: Ideal if you don't need advanced features and just need a simple editor setup.

Frequently Asked Questions

Q: How does light mode affect existing projects and what features are disabled?

A: In light mode, Pylance does not analyze closed files, perform indexing, extract type information from library code, or provide Pytest support. This reduces resource usage but limits IntelliSense features like auto-import suggestions, workspace-wide code navigation, find all references, and multi-file rename. Editor features such as completion, hover, and go-to definition will still work, but third-party library symbols may be unavailable if stubs or type information are missing, which can also affect diagnostics.

Q: Can I customize individual settings after switching to light mode?

A: Yes, you can individually override any of the settings adjusted by languageServerMode. For example, you can re-enable indexing or Pytest support by explicitly setting those configurations in your settings.json.

Q: Is light mode suitable for all types of development?

A: Light mode is ideal for large projects, systems with limited resources, or when you require a lightweight editing experience. If you need comprehensive IntelliSense and code analysis across your entire workspace, default mode is recommended.

Q: How do I know if I should switch to light mode?

A: If you experience performance issues, such as high memory or CPU usage, slow editor responses, or lag in IntelliSense features, trying light mode may help. You can monitor system performance and adjust settings as needed.

For more information on Pylance settings and customization, refer to the Pylance Settings and Customization documentation.

This document was generated with the assistance of AI and has been reviewed by humans for accuracy and completeness.