jamesStr

Если понял правильно:

from typing import Optional

def freq(arr: list, digit: int = 1) -> Optional[float]:
    count = 1
    res = []
    for x in arr:
        if x == digit:
            res.append(count)
            count = 0
        count += 1
    try:
        return sum(res) / len(res)
    except ZeroDivisionError:
        return None

a = [0, 0, 0, 0, 1, 0, 0, 0, 0, 1]
print(a, ' --> ', freq(a))

a = [0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0]
print(a, ' --> ', freq(a))

# [0, 0, 0, 0, 1, 0, 0, 0, 0, 1] --> 5.0
# [0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0] --> 3.142857142857143