from timeit import timeit

code1 = """
a = []

for _ in range(10 ** 5):
    a.append(_)
    length = len(a)
"""

code2 = """
length = 0
a = []

for _ in range(10 ** 5):
    a.append(_)
    length += 1
"""

print(timeit(code1, number=1000))
print(timeit(code2, number=1000))

"""

code1 average: 85.2417806898866
code2 average: 59.88997145998508

"""