Using Python LSP

Overview

The pyright-lsp plugin provides semantic code intelligence for Python. Use LSP tools instead of grep/read when you need semantic accuracy - LSP understands Python's type system, inheritance, and symbol relationships.

When to Use LSP vs Text Search

digraph lsp_decision {
    "Need code info?" [shape=diamond];
    "Semantic accuracy needed?" [shape=diamond];
    "Use LSP tool" [shape=box];
    "Use Grep/Read" [shape=box];

    "Need code info?" -> "Semantic accuracy needed?" [label="yes"];
    "Need code info?" -> "Use Grep/Read" [label="no - text patterns"];
    "Semantic accuracy needed?" -> "Use LSP tool" [label="yes"];
    "Semantic accuracy needed?" -> "Use Grep/Read" [label="no"];
}

Use LSP for:

• Finding all usages before refactoring
• Getting type information
• Navigating to definitions
• Checking for type errors

Use Grep for:

• Text patterns (comments, strings, config)
• Cross-language searches
• When LSP unavailable

LSP Operations Quick Reference

Task	LSP Operation	Instead of
Find all callers of a method	findReferences	Grep for method name
Get function return type	hover	Read file + parse
Jump to definition	goToDefinition	Grep + Read
Check type errors	getDiagnostics	Run mypy/pyright CLI
View file structure	documentSymbol	Read entire file

Key Patterns

Before Refactoring: Find All References

Wrong approach:

Grep for "method_name" -> may miss aliased calls, get false positives

Right approach:

LSP findReferences on method -> gets ALL semantic usages, no false positives

Getting Type Information

Wrong approach:

Read file -> find function -> parse return annotation manually

Right approach:

LSP hover on symbol -> instant type signature with docs

Verifying Type Correctness

Wrong approach:

Bash: pipx run mypy src/ (slow, external tool)

Right approach:

LSP getDiagnostics on changed files -> instant, no external process

Common Mistakes

Mistake	Why It's Wrong	Fix
Grep for symbol before rename	Text search misses method calls through aliases, inheritance	Use findReferences
Read entire file for one type	Wastes context, slow	Use hover
Run mypy after every change	Slow, requires external tool	Use getDiagnostics
Grep to find definition	May find wrong match (same name, different module)	Use goToDefinition

How LSP Tools Work

LSP is a built-in Claude Code tool, not a bash command. When pyright-lsp plugin is enabled, Claude Code automatically provides these operations:

• goToDefinition - navigate to where symbol is defined
• findReferences - find all usages of a symbol
• hover - get type signature and documentation
• getDiagnostics - get type errors for a file
• documentSymbol - list all symbols in a file

You invoke these through Claude's tool system, not via bash. If LSP is unavailable, fall back to grep/read but document the limitation.

Prerequisites

1. Plugin enabled: pyright-lsp@claude-plugins-official in ~/.claude/settings.json
2. Pyright installed: pip install pyright or npm install -g pyright
3. Project configured: pyproject.toml or pyrightconfig.json present (recommended)

Fallback Strategy

If LSP is unavailable (tool not found, server not running):

1. Document the limitation - note that you're using text search as fallback
2. Use Grep with caution - understand it may miss aliased calls or inheritance
3. Verify manually - for refactoring, double-check results make sense semantically
4. Suggest fix - remind user to ensure pyright is installed and plugin enabled

Red Flags - Stop and Use LSP

These thoughts mean you should use LSP, not grep:

Thought	Reality
"Let me grep for this function"	If it's a symbol, use findReferences
"I'll read the file to find the type"	Use hover for instant type info
"Let me run mypy to check"	Use getDiagnostics - faster, no subprocess
"I'll search for where this is defined"	Use goToDefinition - semantic accuracy
"Grep is faster for quick searches"	LSP is 900x faster for semantic queries

When LSP Won't Help

• No pyright binary installed
• Working with dynamic Python (heavy eval, exec, __getattr__)
• Cross-language references
• Comment/docstring searches
• Projects without type hints (LSP works but limited value)