Mathics3-trepan 1.0.2

Mathics3 Module Examples

To enable debugging in Mathics3, install mathics3-trepan. Inside a mathics3 session run:

In[1]:= LoadModule["pymathics.trepan"]
Out[1]= "pymathics.trepan"

Next, you need to active some events to trigger going into the debugger:

In[2]:= DebugActivate[mpmath->True]
Out[2]=

Other events include: “Debugger”, “Get”, “Numpy”, “SymPy”, “apply”, “evalMethod”, and “evaluation”.

In the above, mpmath->True goes into the debugger anytime a mpmath function is called. Exp[1.0] is such a function:

In[3]:= Exp[1.0]
mpmath call  : mpmath.ctx_base.StandardBaseContext.power(2.718281828459045, 1.0)
(/tmp/mathics-core/mathics/eval/arithmetic.py:68 @88): run_mpmath
mp 68             result_mp = tracing.run_mpmath(mpmath_function, *mpmath_args)
(Mathics3 Debug)

A useful command to run is bt -b which shows the Buitin Function calls in the call stack:

(Mathics3 Debug) bt -b
B#0 (2) Power[z__]
          called from file '/tmp/mathics-core/mathics/core/builtin.py' at line 659
B#1 (3) Power[x_, y_]
          called from file '/tmp/mathics-core/mathics/builtin/arithfns/basic.py' at line 477

To get a list of all debugger commands:

(Mathics3 Debug) help *
List of all debugger commands:
    alias      down   help  mathics3      reload  trepan3k
    backtrace  eval   info  printelement  set     up
    continue   frame  kill  python        show

When you are done inspecting things, run continue (or short-hand c) to resume execution:

(Mathics3 Debug) c
mpmath result: 2.71828182845905
Out[3]= 2.71828

Improved TraceEvaluation

As before, install mathics3-trepan. To set up tracing .evaluate() calls:

In[1]:= LoadModule["pymathics.trepan"]
Out[1]= "pymathics.trepan"

In[2]:= TraceActivate[evaluation->True]
Out[2]=

In contrast to DebugActivate, TraceActivate just prints or traces events.

Now we are ready for some action:

Above we trace before an evaluate() method call and also sometimes show the return value.

To reduce the unnecessary output, evaluations when it has some value. In particular, above there is an evaluation of the Symbols “Power”, and “Plus”, The result of evaluating these is the same symbol. So we don’t show either Evaluating: Power``or ``Returning: Power. Similarly, we omit the same for Plus.

We also omit Returning: Plus[1, x] because Plus[1, x] is the same expression as went in. But notice we do show Returning: Plus[x, 1] = Plus[1, x]. Here the difference is that the order of the parameters got rearranged. Perhaps this is not interesting either, but currently, it is shown.

Now let’s do the same thing but set the value of x:

In[4]:= x = 3
Evaluating: Set[x, 3]

Returning: Set[x, 3] = 3

Out[4]= 3

In[5]:= (x + 1) ^ 2
Evaluating: Power[Plus[x, 1], 2]

  Evaluating: Plus[x, 1]

    Returning: x = 3

  Returning: Plus[x, 1] = 4

Returning: Power[Plus[x, 1], 2] = 16

Out[5]= 16

Here, the return values have the computed Integer values from evaluation as you’d expect to see when working with Integer values instead of mixed symbolic and Integer values.

Post-mortem debugging

To enter the debugger on an unrecoverable error, use the --post-mortem option when invoking mathics:

mathics --post-mortem
# Find a Python bug in Mathics3 and trigger that.
# I modified Compress.eval() and added 1/0

In[1]:= Compress["abc"]
  Traceback (most recent call last):
  File "/tmp/mathicsscript", line 8, in <module>
  sys.exit(main())
           ^^^^^
  ...
  ZeroDivisionError: division by zero
  Uncaught exception. Entering post-mortem debugger...
  (/tmp/mathics/builtin/compress.py:37 @6): eval
  !! 37         1/0
  R=> (<class 'ZeroDivisionError'>, ZeroDivisionError('division by zero'),
  (Trepan3k:pm) load trepan3k_mathics3
  loaded command: "mathics3"
  loaded command: "mbacktrace"
  loaded command: "mup"
  loaded command: "printelement"
  (Trepan3k:pm) mbt -b
  B>0 (0) Compress[expr_, OptionsPattern[Compress]]
            called from file '/tmp/Mathics3/mathics-core/mathics/builtin/compress.py' at line 37
  B>1 (36) Compress[expr_, OptionsPattern[Compress]]
             called from file '/tmp/Mathics3/mathics-core/mathics/builtin/compress.py' at line 37
  (Trepan3k:pm)

Showing Tracebacks on long-running operations

The debugger (and trepan3k) support signal handling. With this, you can set up a SIGINT handler.

Here is an example:

Without the debugger, but with trepan3k installed, you can use Breakpoint[], and issue the handle command. You won’t get as nice of a traceback, but it should still work.