reproduction script below. In the last print statement, it shows me a list with items in it, but with a length of 0

def generator():
	l = []
	yield l
	l.append(1)
	# this correctly prints 1
	print(len(l))

# this should print [([1], 1)], but actually gives [([1], 0)]
print([(l, len(l)) for l in generator()])

when you yield, the list is empty, in this case, the length of your list is just 0 and not 1.

At the time the len function in list comprehension is called .append has not executed, the len call in list comprehension operates on object as it is, whereas the object itself is only referenced rather than copied. If you were to copy the yielded list, then a more expected behaviour of returning [([], 0)] would be demonstrated.