Allow to extend existent recipes

[baitcode]

I've got simple_booking recipe and I want to make complex_booking recipe by simple override of few fields, currently, I have to do:

simple_booking = Recipe(Booking,
  name = 'Ilya', price=100,
)
complex_booking = Recipe(Booking,
  name = 'Ilya', price=100, does_complex_stuff = True
)

preferred syntax would be:

simple_booking = Recipe(Booking,
  name = 'Ilya', price=100,
)
complex_booking = simple_booking.extend(
  does_complex_stuff = True
)

So I monkey patched mommy with:

# Monkey patch
def extend(self, **attrs):
    attr_mapping = self.attr_mapping.copy()
    attr_mapping.update(attrs)
    return Recipe(self.model, **attr_mapping)

Recipe.extend = extend

But monkey patching is inconvenient. Any chance that you'll implement something like this? Or you want to me make pull request with that code?

[vandersonmota]

Indeed. I rather have an extend method in the Recipe class. If you're going to send the PR, don't forget to add tests and docs.

thanks