faulthandler

Faulthandler is a Python standard library module that provides facilities for printing Python stack traces to help diagnose crashes, hangs, and deadlocks in Python programs. It is designed to offer quick visibility into what multiple threads are doing at the moment a fault occurs or on demand, without a full debugger.

The module can emit tracebacks for the current thread or for all threads, and it can include local variables when requested. Output is written to a file-like object, with the default being standard error. Faulthandler can be enabled to install fault-dumping behavior that activates automatically on fatal errors, or it can be used explicitly to dump tracebacks at a chosen moment.

On Unix-like systems, faulthandler can be configured to dump tracebacks in response to signals (for example, by receiving a specific signal such as SIGUSR1), enabling operators to inspect a running process without restarting it. The functionality is designed to be lightweight and non-intrusive, making it suitable for production use in long-running services and background workers.

Usage in brief involves importing the module and enabling it, then calling the available dump routines as needed. It is capable of showing the Python-level call stacks of threads, though it does not reveal internal details inside C extensions beyond what the Python interpreter exposes. While not a replacement for a full debugger, faulthandler is a widely used diagnostic aid that helps developers gather actionable information during faults and performance issues in multi-threaded Python applications.