How to Debug Running Python Applications with On-the-Fly Stack Traces?

Debug Running Python Applications with On-the-Fly Stack Trace

Encountering occasional application freezes can be frustrating when troubleshooting the root cause. Python provides a mechanism to generate a real-time stack trace, allowing you to inspect the currently executing code and identify the problematic spot.

Solution using Signal Handling

To obtain an on-the-fly stack trace, consider utilizing the following code:

<code class="python">import code, traceback, signal

def debug(sig, frame):
    d={'_frame':frame}         # Allow access to frame object.
    d.update(frame.f_globals)  # Unless shadowed by global
    d.update(frame.f_locals)

    i = code.InteractiveConsole(d)
    message  = "Signal received : entering python shell.\nTraceback:\n"
    message += ''.join(traceback.format_stack(frame))
    i.interact(message)

def listen():
    signal.signal(signal.SIGUSR1, debug)  # Register handler

listen()</code>

Usage:

1. Call listen() to enable signal handling.
2. Send a SIGUSR1 signal to the running process using a tool like kill or the Python code: os.kill(pid, signal.SIGUSR1).

This will trigger a Python console with the current stack trace and allow you to explore variables. Press Ctrl-D to resume execution.

Additional Option

For debugging backgrounded processes, consider using a pipe-based solution provided in the Python Cookbook recipe.

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