Python while循环

while循环

while 判断条件(condition)：
    执行语句(statements)……

while循环的跳出

while+break

• 同for循环一样，只要运行到break就会立刻中止本层while循环

i_num, num = 0, 5
while i_num <= num:
    print("loop cycle: %d" % i_num)
    i_num += 1
    if(i_num==2):
        print("break, jump out of the loop")
        break
else:
    print("The loop ends normally")
    
result:
loop cycle: 0
loop cycle: 1
break, jump out of the loop

while+continue

• 同for循环一样，只要运行到continue就会立刻中止本层while循环的本次操作，接着回到while后的条件判断，进行下一次循环语句。

i_num, num = 0, 5
while i_num <= num:
    i_num += 1
    if(i_num==2):
        print("skip this loop cycle")
        continue
    print("loop cycle: %d" % i_num)
else:
    print("The loop ends normally")

while+else

• 当迭代对象完成所有迭代后且此时的迭代对象为空时，则执行else子句；如果迭代对象因为某种原因（如带有break关键字）提前退出迭代，则else子句不会被执行，程序将会直接跳过else子句继续执行后续代码(当乖乖执行完while的所有语句，奖励一个else)

i_num, num = 0, 5
while i_num < num:
    print("loop cycle: %d" % i_num)
    i_num += 1
else:
    print("The loop ends normally")

result:
loop cycle: 0
loop cycle: 1
loop cycle: 2
loop cycle: 3
loop cycle: 4
The loop ends normally

while True

• 死循环，必须在循环体里指定跳出条件

循环嵌套

• for和while循环可以相互嵌套
• break， continue，else也只和本层循环对应

for i in range(1, 4):
    for j in range(1, i + 1):
        print("{}*{}={:<4}".format(j, i, i * j), end="")
    print("")
    
result:
1*1=1   
1*2=2   2*2=4   
1*3=3   2*3=6   3*3=9