Using flake8 with multiple dispatch

[oscarbenjamin]

There are many flake8 errors in sets like:

sympy/sets/handlers/intersection.py:14:1: F811 redefinition of unused 'intersection_sets' from line 10
sympy/sets/handlers/intersection.py:18:1: F811 redefinition of unused 'intersection_sets' from line 14
sympy/sets/handlers/intersection.py:22:1: F811 redefinition of unused 'intersection_sets' from line 18
...

These are because the same function name is used repeatedly in multiple dispatch:

sympy/sympy/sets/handlers/intersection.py

Lines 10 to 20 in be9bba3

	@dispatch(ConditionSet, ConditionSet)
	def intersection_sets(a, b):
	return None
	@dispatch(ConditionSet, Set)
	def intersection_sets(a, b):
	return ConditionSet(a.sym, a.condition, Intersection(a.base_set, b))
	@dispatch(Naturals, Integers)
	def intersection_sets(a, b):
	return a

Is there a good way to tell flake8 that these are fine?

[ethankward]

Maybe this would help, once we're able to use type annotations?

[asmeurer]

Is it possible to use different function names with multiple dispatch? IMO a cleaner API would be to name each function like intersection_sets_Naturals_Integers and so on. That would also make the individual functions available for debugging. But presumably @dispatch determines which function to add the dispatch to based on its name.

[oscarbenjamin]

There is a pattern that flake8 understands which is often used for single dispatch:

from sympy.multipledispatch import Dispatcher

do_stuff = Dispatcher('do_stuff')

@do_stuff.register(int)
def _(arg):
    return -arg

@do_stuff.register(float)
def _(arg):
    return 2*arg

print(do_stuff(2))
print(do_stuff(2.0))

Here flake8 does not complain about the name _ being reused. On the other hand if you want to call the function do_stuff_float etc then you can because used this way multipledispatch does not care what the function name is.