binary search by Python3

def binary_search(number, array=[]):
    """ binary search. """
    low = 0
    high = len(array) - 1
    while low <= high:
        mid = (low + high) // 2
        guess = array[mid]
        if guess == number:
            return mid
        elif guess < number:
            low = mid + 1
        else: #guess > number
            high = mid - 1
    return None

二分查找法 O(logn)