Bug: Thread cleanup exception during interpreter shutdown when using VS Code debugger

まず、提供されたスクリプトを VS Code デバッガーで再現し、通常の python script.py の実行結果と比較します。デバッガーが管理するスレッドと、_DeleteDummyThreadOnDel.__del__ 周辺のインタープリター終了時のクリーンアップを調査します。デバッガーでの実行が報告された TypeError なしで終了すれば完了です。

📌 Environment

• Python Version: 3.13.5
• OS: Windows 11
• Debugger: VS Code (debugpy)

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📝 Description

When running code under the VS Code debugger, an exception is raised during interpreter shutdown:

Exception ignored in: <function _DeleteDummyThreadOnDel.__del__>
Traceback (most recent call last):
  File ".../threading.py", line 1385, in __del__
TypeError: 'NoneType' object does not support the context manager protocol

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🔍 Key Observation

• ❌ Does NOT occur when running normally (python script.py)
• ✅ Only occurs when running via VS Code debugger

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🧪 Steps to Reproduce

from strands import Agent, tool
from strands_tools import http_request
import boto3
from strands.models import BedrockModel

session = boto3.Session(region_name="us-east-1")

model = BedrockModel(
    model_id="your-model-id",
    boto_session=session
)

@tool
def dummy_tool(text: str) -> str:
    return text

agent = Agent(
    system_prompt="Test agent",
    tools=[http_request, dummy_tool],
    model=model
)

agent("Test request")

print("DONE EXECUTION")

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📤 Observed Output (Debugger Only)

DONE EXECUTION
Exception ignored in: <function _DeleteDummyThreadOnDel.__del__>
Traceback (most recent call last):
  File ".../threading.py", line ...
TypeError: 'NoneType' object does not support the context manager protocol

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✅ Expected Behavior

No exception during interpreter shutdown in debugger mode.

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❌ Actual Behavior

Thread cleanup triggers a TypeError during interpreter shutdown when running under debugger.

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📎 Notes

• Likely related to debugger-managed threads and interpreter shutdown order
• Possibly occurs when threads outlive global state during teardown
• Does not impact runtime correctness

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🛠️ Workarounds

• Running script outside debugger avoids issue
• Adding delays (time.sleep) reduces occurrence but does not fully eliminate

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📌 Summary

This appears to be a debugger-related threading cleanup issue during interpreter shutdown in Python 3.13.