Hi all,
I'm looking at CPython's behavior when an addition is called. From what
I understand, binary_op1
<https://github.com/python/cpython/blob/3.8/Objects/abstract.c#L786> is
eventually called, and it calls either slotv or slotw, which seems to be
the binaryfunc defined as nb_add in the field tp_as_number of
respectively v / w.
I have a few questions:
1) In the default case, tp_as_number->nb_add is defined by the function
slot_nb_add
<https://github.com/python/cpython/blob/3.8/Objects/typeobject.c#L6312>
itself stemming from the macro expansion SLOT1BINFULL
<https://github.com/python/cpython/blob/3.8/Objects/typeobject.c#L6140>
defined in typeobject.c. Both binary_op1(v, w) and slot_nb_add(v, w)
appear to perform similar checks (if their second argument is a subtype
of the first, etc), to decide if v's add or w's reverse add must be
called and in which order. I find this repetition weird, and I guess I'm
missing something... Any ideas?
2) From the SLOT1BINFULL macro, both __add__ and __radd__ are defined by
the slot_nb_add function (with some argument swapping done by
wrap_binaryfunc_l / wrap_binaryfunc_r). If I want to define a different
behavior for the reverse operator during a definition with a
PyTypeObject, I guess I should add an "__radd__" method?
3) If I create a user-defined class A, having different methods __add__
and __radd__, these methods are added in A's dictionary. From what I
understand, the function update_one_slot
<https://github.com/python/cpython/blob/3.8/Objects/typeobject.c#L7209>
is then called to change A's tp_as_number->nb_add to point to the
methods defined by __add__ and __radd__? From the code documentation, I
think that "a wrapper for the special methods is installed". Where
exactly is this wrapper applied, and how does it know when to dispatch
to __add__ or __radd__?
Kind regards,
Raphaël
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