Error Handling and Console Output in the Hybrid Async-Native Engine for Python

#hejhdiss

Author: @hejhdiss (Muhammed Shafin P)

Original Concept Reference: Hybrid Async-Native Engine for Python – Design Concept

Introduction

In a hybrid Python/C execution model, managing errors and console output consistently is crucial. The engine ensures Python coroutines propagate exceptions naturally, while C threads execute safely in parallel. Additionally, any output from C threads is sent directly to the console as intended.

Python Coroutine Error Handling

Errors raised inside Python coroutines behave exactly like standard Python exceptions.
When a coroutine submitted via spawn() fails, the exception is captured by its Future.
Awaiting the Future raises the original exception at the call site.
Multiple awaits on the same Future propagate the same exception consistently.

Example (descriptive):

A Python coroutine fetches data from a URL. If a network error occurs, ConnectionError is raised when the Future is awaited. All other awaits on the same Future will see the same exception.

✅ Key point: Python’s exception model is fully preserved for coroutines.

C Task Error Handling

Non-GIL C threads cannot raise Python exceptions directly.
Errors in C tasks are wrapped in a custom exception object (CExecutionError).
When Python checks the result or waits for completion, the engine raises this exception at the original Python call site.
This preserves parallel execution safety while giving Python developers natural error handling.

Example (descriptive):

A C thread calculates a matrix inverse. If the matrix is singular, it generates a CExecutionError. When Python accesses the result, the exception is raised at the line where the task was submitted, allowing Python to handle it with try/except blocks.

✅ Key point: C task errors are delayed until Python checks results, ensuring safe Non-GIL execution.

Console Output from C Threads

Any standard output (stdout) or console prints generated by C threads appear directly in the console.
This behavior is intentional: C threads can log or display information immediately without waiting for Python to process it.
Python developers should be aware that console output may interleave with Python prints if multiple threads are writing simultaneously.

Example (descriptive):

A C thread performs data preprocessing and prints progress updates. These updates appear directly in the console in real time, independent of Python’s execution.

Error Propagation Summary

Task Type	Exception Propagation	Raised At	Notes
Python Coroutine	Standard Python exception	Await or Future result	Supports multiple awaits; preserves traceback
C Function	Custom `CExecutionError` wrapper	Spawn/call site in Python	Safe for Non-GIL execution; traceback includes task origin
Hybrid Tasks	Depends on underlying type	Appropriate context	Python awaits or checks results; C errors wrapped

Design Rationale

Isolation: Non-GIL threads do not manipulate Python interpreter state, preventing memory corruption.
Safety: Error propagation is delayed until Python accesses results, avoiding interference with parallel execution.
Traceability: Exceptions include the Python call site, making debugging easier.
Direct Console Output: C threads can print to stdout for progress logging or debugging, independent of Python execution.

Example workflow (descriptive):

Python submits a C task to preprocess data.
C thread encounters an invalid input → generates CExecutionError.
Python accesses result → CExecutionError is raised at submission line.
Simultaneously, C thread progress prints appear in the console in real time.

Summary

Python coroutines: exceptions behave normally, fully integrated with Python memory and traceback.
C tasks: errors are wrapped in a custom object and raised at the Python call site when results are accessed.
C stdout/console prints: appear directly in real time, independent of Python execution.
Goal: ensure Python consistency, safe parallel C execution, and real-time logging/output.

This article complements the main design post by explaining error handling and console behavior across Python and Non-GIL C threads, making the engine safe, traceable, and predictable.