Ability to register a non-static type resolution function and a multi-purpose loop

[hameerabbasi]

Let's suppose you want to define a gufunc from within Python. We need two parts: The type resolution function, and the actual loop. So for example:

def typeres(*input_types):
    # Perform some operation with input types.
    return output_types

def loop(*all_allocated_arrays):
    # Perform all operations, store in last arrray(s) as output.

For example, divmod:

def typeres(*input_types):
    if len(input_types) != 2 or not all(t.fits('... * int64') for t in input_types):
         raise TypeError('Type resolution error.')
    return 'int64', 'int64'

def loop(in1, in2, out1, out2):
    out1 = in1 / in2
    out2 = in1 % in2

divmod = define_gufunc(typeres, loop)

So, the type resolution function will be called and then all the output arrays allocated. Let's say we pass in two 5 * int64 arrays. And then, loop gets passed in all four 5 * int64 arrays, and there's no looping in Python, only in C.

Then, what happens is: out1, out2 is returned from the gufunc.

[skrah]

It looks like the example relies on the primitives // and %, so that would be already possible:

>>> def f(a, b):
...     out1 = a // b
...     out2 = a % b
...     return out1, out2
... 
>>> x = array([8, 9, 10])
>>> y = array([3, 4, 5])
>>> f(x, y)
(array([2, 2, 2], type='3 * int64'), array([2, 1, 0], type='3 * int64')

[hameerabbasi]

This is a simple example of how to define a gufunc from Python. It'd be nice to have this be possible in general.