def sum(x, y):
	"""Sum x and y

	>>> sum(10, 20)
	30

	>>> sum(-10, 20)
	10

	>>> sum('10', 20)
	Traceback (most recent call last):
	...
	AssertionError: x needs to be in or float
	"""

	assert isinstance(x, (int, float)), 'x needs to be in or float'
	assert isinstance(y, (int, float)), 'x needs to be in or float'

	return x + y