痛饮通过 Python 日期时间 object 到 C++

Question

I have a function in C++ that is passed a uint64_t as nanoseconds from epoch. I have wrapped this number in an object DateTime as in

struct DateTime {
    uint64_t epochns;
};
void print( DateTime ts );

Obviously the function is not exactly print as I could use Python's own for this purpose.

It is important that I use it seamlessly with Python datetime objects as in

print( datetime(1985,7,1) )

I'm unsure how to write a typemap that achieves this requirement.

Any hints?

Answer 1

Call the method datetime.timestamp on the object to return the epoch in seconds then multiply by 1E6 to get to microseconds and round to integer. Then multiply again by 1000 to get to nanoseconds.

%typemap(in)  DateTime
{
    PyObject* str = PyString_FromString( "timestamp" );
    PyObject* obj = PyObject_CallMethodObjArgs( $input, str, nullptr );
    $1.epochns = int64_t(PyFloat_AsDouble( obj )*1000000)*1000LL;
    Py_XDECREF( obj );
    Py_XDECREF( str );
}

The intermediate multiplication is necessary as if you multiply straight by 1E9 you will have unrounded garbage in the nanoseconds part.