三段组合成一条线

再把"求和"接到后面，三段组合成一个函数：

A = [120, 80, 200, 150]
LINE = 100

def compose(f, g):
    """先做 g，再把结果交给 f"""
    return lambda x: f(g(x))

keep = lambda xs: [a for a in xs if a >= LINE]
x10  = lambda xs: [a * 10 for a in xs]

total = lambda xs: sum(xs)
line3 = compose(total, compose(x10, keep))
print(line3(A))