REF: use datetime C API instead of getattrs

[jbrockmendel]

@WillAyd i think there are a couple of paths that must not be reached, since it looks like they pass np.datetime64 objects to these pydatetime-requiring functions. in python/cython id check that with an assert False. have a favorite way of doing that in c code?

[WillAyd]

I like the idea think we need to approach the implementation differently though

[WillAyd]

Looking at the cpython source the datetime library seems to be implemented as a capsule. There's some documentaiton on that here:

https://docs.python.org/3/extending/extending.html#providing-a-c-api-for-an-extension-module

I really don't want to keep scattering these imports throughout the code base because it goes against the CPython documentation - can you check if the capsule approach would work?

[WillAyd]

Make sure to avoid blind casting - these should all be preceded by a PyDate_Check call with appropriate error handling, otherwise its anybody guess what happens when you pass the wrong object type to this

[jbrockmendel]

so something like

    PyDateTime_IMPORT;
    if (!PyDate_Check(obj)) {
        PyErr_SetString(PyExc_ValueError,
                        "Object is not a datetime.date object");
        return NULL;
    }
    PyDateTime_Date *dtobj = (PyDateTime_Date*)obj;

    ret = convert_pydatetime_to_datetimestruct(dtobj, &dts);

[jbrockmendel]

So in objToJSON.c L1552 we call PyDateTimeToEpoch but IIUC obj ther eis a np.datetime64 object, not a pydatetime object. Isn't that call doomed to failure?

[WillAyd]

Yea you have got the right idea with that error handling - nice job

[WillAyd]

If that is the case I think that behavior would be undefined, so could segfault or get garbage values. Do you know of a reproducer?

[WillAyd]

Is this cast necessary?

[jbrockmendel]

without it i see a bunch of warnings

warning: incompatible pointer types passing 'PyDateTime_DateTime *' to parameter of type 'PyObject *' (aka 'struct _object *') [-Wincompatible-pointer-types]
        PyObject *offset = extract_utc_offset(obj);

[WillAyd]

Gotcha makes sense

[jbrockmendel]

it works locally, but im seeing build failures from the type checking

[jbrockmendel]

Closing as not worth the trouble.