#!/usr/bin/python3

#杨辉三角（只打印6层）

  #       1

  #      1 1

  #     1 2 1

  #    1 3 3 1

  #   1 4 6 4 1

  # 1 5 10 10 5 1′

#循环：

def Pascals_triangle(max):

    t=[1]

    n=1

    while n<=max:

        s=” “.join(str(t))

        print(s.center(40))

        L=t.copy()

        for i in range(1,len(t)):

            L[i]=t[i]+t[i-1]

        L.append(1)

        t=L

        n+=1

Pascals_triangle(6)

# 生成器：

def Pascals_triangle(n):

    l=[1]

    while True:

        s=” “.join(str(l))

        yield(s.center(40))

        l=[l[x]+l[x+1] for x in range(len(l)-1)]

        l[0:0]=[1]

        l.append(1)

        if len(l)>n:

            break

gen=Pascals_triangle(6)

it=iter(gen)

while True:

    try:

        x=next(it)

        print(x)

    except StopIteration:

        break