python 用加法实现a,b两数相乘

"""
思路:1.a * b = a + a + a + ...
　　 2.a * b = n个a相加,只需求证b = n即可
　　 3.用for 循环遍历即可,b就是range的最大次数
　　 4.需考虑a,b有五种情况存在,但结果会有三种,正数,0,负数
"""

def  multiplication(a,b):
    if a > 0 and b > 0:
        sum = 0
 for i in range(b):
 sum += a
 print(sum)
 elif a < 0 and b < 0:
 sum = 0
 for i in range(-b):
 sum += a
 sum = -sum
 print(sum)
 elif a > 0 and b < 0:
 sum = 0
 for i in range(-b):
 sum += a
 print(-sum)
 elif a < 0 and b > 0:
 sum = 0
 for i in range(b):
 sum += a
 print(sum)
 else:
 sum = 0
 print(sum)
multiplication(8,5) #输出结果40
multiplication(-8,-5) #输出结果40
multiplication(8,-5) #输出结果-40
multiplication(-8,5) #输出结果-40
multiplication(0,-5) #输出结果0
multiplication(8,0) #输出结果0