这次提交加了几行

第 3 次提交（加上减法）之后文件有 4 行，第 4 次提交（加上除法）之后有 6 行。运行下面这段程序：

def diff(old, new):
    added = [l for l in new if l not in old]
    removed = [l for l in old if l not in new]
    return len(added), len(removed)

old = ['def add(a, b):', '    return a + b',
        'def sub(a, b):', '    return a - b']
new = ['def add(a, b):', '    return a + b',
        'def sub(a, b):', '    return a - b',
        'def div(a, b):', '    return a / b']
a, r = diff(old, new)
print(str(a) + "/" + str(r))