[Python-Dev] sys.settrace does not produce events for C functions

[Pablo Galindo Salgado]

The docs for sys.settrace mention that:

>> event is a string: 'call', 'line', 'return', 'exception', >> 'c_call',
'c_return', or 'c_exception'

But in the code for ceval.c the only point where call_trace is invoked with
PyTrace_C_CALL or PyTrace_C_RETURN is under the C_TRACE macro. In this
macro this line prevents any function set up using sys.settrace to call
call_trace with the mentioned arguments:

if (tstate->use_tracing && tstate->c_profilefunc)

Notice that from the code of PyEval_SetTrace and PyEval_SetProfile, only
the later sets tstate->c_profilefunc and therefore only functions installed
using sys.setprofile will recieve a c_call for the event.

Xiang Zhan has suggested me to ask here what is the best course of action:

1) Document this behavior.

2) Fix the code.

This question is related to this issue:
https://bugs.python.org/issue17799

Thanks everyone for your time!

Pablo
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