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The SDK was experiencing deadlocks when MCP servers produced verbose stderr output. The issue occurred because: 1. The SDK read stdout and stderr sequentially (stdout first, then stderr) 2. When stderr buffer filled up (64KB on Linux, 16KB on macOS), the subprocess would block trying to write more to stderr 3. Since the subprocess was blocked, it couldn't write to stdout 4. The parent process was waiting for stdout, creating a deadlock This fix redirects stderr to a temporary file instead of a pipe, which: - Eliminates the pipe buffer limitation (files have no such restriction) - Prevents any possibility of deadlock - Still captures stderr for error reporting (keeping last 100 lines) - Works consistently across all async backends (asyncio, trio, etc.) The temp file is automatically cleaned up when the subprocess ends, and we use a circular buffer (deque) to keep only the last 100 lines in memory for error reporting purposes. Fixes deadlock issue reported in Slack where SDK would hang indefinitely when receiving messages from MCP servers. 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com> |
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| examples | ||
| scripts | ||
| src/claude_code_sdk | ||
| tests | ||
| .gitignore | ||
| CHANGELOG.md | ||
| CLAUDE.md | ||
| LICENSE | ||
| pyproject.toml | ||
| README.md | ||
Claude Code SDK for Python
Python SDK for Claude Code. See the Claude Code SDK documentation for more information.
Installation
pip install claude-code-sdk
Prerequisites:
- Python 3.10+
- Node.js
- Claude Code:
npm install -g @anthropic-ai/claude-code
Quick Start
import anyio
from claude_code_sdk import query
async def main():
async for message in query(prompt="What is 2 + 2?"):
print(message)
anyio.run(main)
Usage
Basic Query
from claude_code_sdk import query, ClaudeCodeOptions, AssistantMessage, TextBlock
# Simple query
async for message in query(prompt="Hello Claude"):
if isinstance(message, AssistantMessage):
for block in message.content:
if isinstance(block, TextBlock):
print(block.text)
# With options
options = ClaudeCodeOptions(
system_prompt="You are a helpful assistant",
max_turns=1
)
async for message in query(prompt="Tell me a joke", options=options):
print(message)
Using Tools
options = ClaudeCodeOptions(
allowed_tools=["Read", "Write", "Bash"],
permission_mode='acceptEdits' # auto-accept file edits
)
async for message in query(
prompt="Create a hello.py file",
options=options
):
# Process tool use and results
pass
Working Directory
from pathlib import Path
options = ClaudeCodeOptions(
cwd="/path/to/project" # or Path("/path/to/project")
)
API Reference
query(prompt, options=None)
Main async function for querying Claude.
Parameters:
prompt(str): The prompt to send to Claudeoptions(ClaudeCodeOptions): Optional configuration
Returns: AsyncIterator[Message] - Stream of response messages
Types
See src/claude_code_sdk/types.py for complete type definitions:
ClaudeCodeOptions- Configuration optionsAssistantMessage,UserMessage,SystemMessage,ResultMessage- Message typesTextBlock,ToolUseBlock,ToolResultBlock- Content blocks
Error Handling
from claude_code_sdk import (
ClaudeSDKError, # Base error
CLINotFoundError, # Claude Code not installed
CLIConnectionError, # Connection issues
ProcessError, # Process failed
CLIJSONDecodeError, # JSON parsing issues
)
try:
async for message in query(prompt="Hello"):
pass
except CLINotFoundError:
print("Please install Claude Code")
except ProcessError as e:
print(f"Process failed with exit code: {e.exit_code}")
except CLIJSONDecodeError as e:
print(f"Failed to parse response: {e}")
See src/claude_code_sdk/_errors.py for all error types.
Available Tools
See the Claude Code documentation for a complete list of available tools.
Examples
See examples/quick_start.py for a complete working example.
License
MIT