bqm.resize should not return a value

[JoelPasvolsky]

Description
(

dimod/dimod/binary/binary_quadratic_model.py

Line 1600 in 220a22a

return self.data.resize

) :

return self.data.resize

returns a zero when this method is run. Why?

Steps To Reproduce

bqm.resize(3)
0

Expected Behavior
Quietly do its work.

Environment

• OS: WIN10
• Python version: 3.6

Additional Context
I'm in that file now, can I delete the return ?

[arcondello]

We need to return a value in order to be able to raise an exception. See error return values.

We could obfuscate it, but that would result in a performance regression since this function is called frequently.

[JoelPasvolsky]

What about returning the difference in number of variables between current and previous BQM rather than 0?

[arcondello]

Also, to be clear,

dimod/dimod/binary/binary_quadratic_model.py

Line 1600 in 220a22a

return self.data.resize

does not return the value of zero, it is returning the method to be used. See

dimod/dimod/decorators.py

Line 406 in 220a22a

def forwarding_method(func):

The value is returned by

dimod/dimod/binary/cybqm/cybqm_template.pyx.pxi

Line 713 in 220a22a

cpdef Py_ssize_t resize(self, Py_ssize_t n) except -1:

which is a cpdef function which is why we need that return value.

[arcondello]

What about returning the difference in number of variables between current and previous BQM rather than 0?

Could just be the size of the resulting BQM (since -1 is what indicates an error). It's a bit redundant since that's the value being passed in but at least would be a bit more meaningful 🤷

[arcondello]

What about returning the difference in number of variables between current and previous BQM rather than 0?

Changed my mind, your idea is better. We can just error on 0 instead since that should be an uncommon case if we're returning the delta.