Breakpoint[]This can be used for debugging the Mathics3 implementation, but if you are familiar with Python, it might assist in debugging a Mathics3 programs as well.
By default, the Python debugger (pdb) is loaded. For loading other debuggers, change the environment variable PYTHONBREAKPOINT.
Mathics3 code includes a breakpoint handler function, mathics.disabled_breakpoint which reports whether Breakpoint[] was encountered in Mathics3, or breakpoint() was encountered in the Mathics3 source code. In contrast to pdb, trepan3k and other handlers, this breakpoint handler does not stop inside, it just reports.
Here is how to use mathics.disabled_breakpoint:
SetEnvironment["PYTHONBREAKPOINT" -> "mathics.disabled_breakpoint"];
Breakpoint[]
The environment variable PYTHONBREAKPOINT can be changed at runtime to switch breakpoint() and Breakpoint[] behavior.