How

CPython itself maintains a list of signal handles, defined as Handlers macro

signal.signal function (signal_signal_impl in C) modifies Handlers list (PyOS_setsig and PyOS_getsig take the responsibility to call signal function from <signal.h>).

then it passes signal_handler to PyOS_setsig for any callable.

Once a signal is raised, signal_handler will be called,

in which trip_signal is called, setting tripped flag.

Then who does the call to the callable?

It’s _PyErr_CheckSignalsTstate

which checks all signalnum in 1..<Py_NSIG, calling its installed callable whose tripped == 1

How is that function above called?

1. PyErr_CheckSignals (declared in pyerrors.h, called manually )
2. handle_signals from Python/ceval_gil.c

← _PyEval_MakePendingCalls ← Py_MakePendingCalls