可以找出元素第一次出现位置的二分查找

binary_search.py

def binary_search(l, t):
    low, high = -1, len(l)
    while low+1 != high:
        mid = (low + high) / 2
        if l[mid] < t:
            low = mid
        else:
            high = mid
    pos = high
    if pos >= len(l) or l[pos] != t:
        pos = -1
    return pos