Issue dragging a pyTag with a message function > Type-/SystemError in R23/Python3 on both Mac&PC.

jochemdk

It took me a while to figure out which part caused the problem converting a scripting tag from py2 to py3...
The console printed the following errors (multiple times at a time):

TypeError: Expected PyCapsule, not None
The above exception was the direct cause of the following exception:
SystemError: PyEval_EvalFrameEx returned a result with an error set

The problem was the message function (I think..). Did a simple test with a pyTag containing only 1 userData button and the following script:

import c4d

def main(): pass

def message(id, data):
    if id == c4d.MSG_DESCRIPTION_COMMAND:
        id2 = data['id'][0].id
        if id2 == c4d.ID_USERDATA:
            userDataId = data['id'][1].id
            if userDataId == 1: tst()

def tst(): print ("tst")

_Copying an object with the pyTag - no problem.
_Yes, the button just prints “tst” in python2 & 3 :}
_Dragging in python2 - no problem.
_Dragging the pyTag to another object (or a duplicate onto itself) in R23 - gives 2 errors

How can I solve this? I guess it's not the wisest idea in the world to put a SystemError in a try-except block...
Tia, Jochem

I saw the following code in the “python3_migration” in the SDK mentioning the "PyCapsule", but It doesn’t make much sense to me :{

PyCObject_AsVoidPtr is replaced by PyCapsule_GetPointer
_next code is only compatible in Python 2.7
P1MSG_UN = msg.GetVoid(c4d.BFM_CORE_PAR1)
pythonapi.PyCObject_AsVoidPtr.restype = c_int
pythonapi.PyCObject_AsVoidPtr.argtypes = [py_object]
P1MSG_EN = pythonapi.PyCObject_AsVoidPtr(P1MSG_UN)

_next code is only compatible in 3.7
P1MSG_UN = msg.GetVoid(c4d.BFM_CORE_PAR1)
P1MSG_EN = pythonapi.PyCapsule_GetPointer(P1MSG_UN, None)

m_adam

Hi @jochemdk, this is an internal bug, nothing you can fix, unfortunately, note that you can ignore them normally the Tag should work as expected.

I've opened a bug report about it.

Cheers,
Maxime.

mikeudin

Have a same issue.
There is a workaround to avoid Error messages?

m_adam

Hi, as a workaround you could add the next code in your message function.

import ctypes

def message(id, data):
    if id == c4d.MSG_DRAGANDDROP:
        ctypes.pythonapi.PyCapsule_New.restype = ctypes.py_object
        capsule = ctypes.pythonapi.PyCapsule_New(b"", b"data", None)
        data["data"] = capsule

Note, this issue may not only affect the Python Tag but any Python BaseList2D which can interact with MSG_DRAGANDDROP, so even your Python TagData could cause the issue.

Keep in mind this is an internal bug, which will be fixed in a future update of Cinema 4D.
Cheers,
Maxime.

mikeudin

Thank you @m_adam!
Here is code for C4D lower vesions support:

import ctypes

def message(id,data):
    
    if id == c4d.MSG_DRAGANDDROP and c4d.GetC4DVersion() >= 23000:
        ctypes.pythonapi.PyCapsule_New.restype = ctypes.py_object
        capsule = ctypes.pythonapi.PyCapsule_New(b"", b"data", None)
        data["data"] = capsule

jochemdk

Thx for your replies! I'll test it soon & hopefully the bug will be fixed :)