count the longest occurence of any number in a list or string

def countOne(s):
    mx=0;cnt=0;
    for i in s:
        if i==1:
            cnt+=1
        else:
            if mx<cnt:
                mx=cnt
            cnt=0
        if mx<cnt:
            mx=cnt
    return mx
Here s is a list s=[0,1,0,1,1,1,0]