python的学习中的难解问题

n=input()
b=ord(n)
a=ord('A')
m=b-a
for i in range(m+1):
    print(' '*(m-i),end='')
    for j in range(a,a+i+1):
        print(chr(j),end='')
    for j in range(a+i-1,a-1,-1):
        print(chr(j),end='')
    print(' '*(m-i))