bsearch

def bsearch(items, x, L=None, R=None):
    if L is None:
        L = 1
    if R is None:
        R = len(items)
    if L > R:
        return None
    mitte = (L + R) // 2
    assert mitte == int(mitte)
    if x < items[mitte-1][1]:
        return bsearch(items, x, L, mitte-1)
    elif x > items[mitte-1][1]:
        return bsearch(items, x, mitte+1, R)
    else:
        return mitte - 1