The debug module

Stack walking, panic backtraces, and talking to a debugger.

debug is a module: bring it in with import debug (and write debug.capture()).

• Backtraces: capture() records the calls that led to the current point, cheaply; Backtrace.frames() resolves each return address to its function and, in a -g build, its source line. print_backtrace() writes the current stack to standard error.
• The debugger: output() writes to the platform’s debugger channel, is_debugger_attached() asks whether a debugger is watching, and breakpoint() stops in it.

A panic prints a backtrace after its message in a build without -O; the PEPPER_BACKTRACE environment variable turns that on (1) or off (0) in any build (see print_backtrace).

Example

import debug;

main(): int {
    var trace = debug.capture();
    var frames = trace.frames();
    assert(frames.count > 0, "main is on the stack");
    debug.output("captured a backtrace");
    return 0;
}

Source: runtime/debug/module.pep