a、求两个数的最大公约数
def common_divisor(a, b):
for i in range(1, min(a, b) + 1):
if a % i == 0 and b % i ==0:
m = i
print ("The common divisor is %d" %m)
一开始对上面这段代码始终没理解，为什么得到是就仅仅是6，因为按照目测，1, 2， 3， 6均符合if的条件，应该都会打印出来。
讨教之后才知道是因为没有区分代码组，print()的位置决定了它最终打印出哪一个m值。
区分一下代码的输出(以common_divisor(12, 18)为例)：
1、
def common_divisor(a, b):
for i in range(1, min(a, b) + 1):
if a % i == 0 and b % i ==0:
m = i
print(i)
print ("The common divisor is %d" %m)
2、
def common_divisor(a, b):
for i in range(1, min(a, b) + 1):
if a % i == 0 and b % i ==0:
m = i
print(i)
print ("The common divisor is %d" %m)
对于1，只有if条件满足的时候，就执行print()语句；而对于2，每执行一次for循环，就执行一次print()；最后，对于开头的代码，（是不是有点穷举的意思。。。），找到所有满足条件的m值，然后打印出最后一个，且只执行一次！！
1、
>>> common_divisor(12, 18)
1
The common divisor is 1
2
The common divisor is 2
3
The common divisor is 3
6
The common divisor is 6
2、
>>> common_divisor(12, 18)
1
The common divisor is 1
2
The common divisor is 2
3
The common divisor is 3
The common divisor is 3
The common divisor is 3
6
The common divisor is 6
The common divisor is 6
The common divisor is 6
The common divisor is 6
The common divisor is 6
The common divisor is 6
The common divisor is 6
b、求两个数的最小公倍数：
def common_mutiple(i, j):
maxnum = max(i, j)
while True:
if maxnum % i == 0 and maxnum % j ==0:
print ("The common mutiple is %d" %maxnum) ##列举，将遇到的第一个满足if条件的maxnum打印出来，然后break，跳出while循环。
break
else:
maxnum = maxnum + 1