Set the system's trace function, which allows you to implement a Python
source code debugger in Python. The function is thread-specific; for a
- debugger to support multiple threads, it must be registered using
- :func:`settrace` for each thread being debugged.
+ debugger to support multiple threads, it must register a trace function using
+ :func:`settrace` for each thread being debugged or use :func:`threading.settrace`.
Trace functions should have three arguments: *frame*, *event*, and
*arg*. *frame* is the current stack frame. *event* is a string: ``'call'``,