7.12_python_lx_day6

一.关键字的使用 pass  break  continue

<1>pass 过(占位)

if 10 == 10:
　　print(123)

while True:
　　pass

<2>break 终止当前循环

 ①打印1~10 遇到5就终止循环

i = 1
while i <=10 :
　　if i == 5:
　　　　break
　　print(i)
　　i+=1

②break 终止的是当前循环

i = 1
while i <= 3:
　　j = 1
　　while j<=3:
　　　　if j == 2:
　　　　　　break
　　　　print(i,j)
　　　　j+=1
　　i+=1

<3>continue 跳过当前循环,从下一次循环开始

①打印1~10 跳过5

i = 1
while i<=10:
	if i == 5:
	　　# 需手动自增加1. 当执行continue时,后面的代码不执行,跳到while循环的条件判断处,会造成死循环
	　　i+=1
	　　continue
	print(i)
	i+=1

②打印1~ 100 所有不含有4的数字

方法一:

i = 1
while i<=100:
	if i // 10 == 4 or i % 10 == 4:
	　　i+=1
	　　continue
	print(i)
	i+=1

方法二:

i = 1
while i <= 100:
	strvar = str(i)
	if "4" in strvar:
	　　i+=1
	　　continue
	print(i)
	i+=1

二.for循环 

<1>遍历,循环,迭代

lst = ["aaa","bbb","ccc","ddd"]
i = 0
while i<len(lst):
　　# 代码的逻辑
　　print(lst[i])
　　i+=1

 for主要用于遍历数据而提出,while在遍历数据时,有局限性

for 变量 in 可迭代对象:
code1
code2
可迭代对象(容器类型数据,range对象,迭代器)

# 遍历字符串
container = "aaa,bbb,ccc"
# 遍历列表
container = ["ddd","eee","fff","hhh"]
# 遍历元组
container = (1,2,3,45)
# 遍历集合
container = {"iii","jjj","kkk","lll","mmm"}
# 遍历字典 (遍历字典时,只遍历键)
container = {"a":1,"b":2,"c":3}

for i in container:
　　print(i)

<2>遍历不等长的二级容器

container = [["aa","bb","cc","dd"],("ee","ff")]
for i in container:
　　# print(i)
　　for j in i:
　　　　print(j)

<3>遍历等长的二级容器

container = [("ab","ac","ad") , ("ef","eg","eh") , ("ij","ik","il") ]
for x,y,z in container:
　　print(a,b,c)
# x,y,z = ("ab","ac","ad")
# x,y,z= ("ef","eg","eh")
# x,y,z = ("ij","ik","il")

<4>range对象

range(开始值,结束值,步长)
结束值本身取不到,取到结束值之前的那个数

①只有一个值  0~9

for i in range(10):
　　print(i)

②只有两个值

for i in range(3,11):
　　print(i)

③只有三个值

for i in range(1,10,3):
　　print(i)

④倒序打印10 ~ 1

for i in range(10,0,-1):
　　print(i)

三:总结

while : 较为复杂的逻辑
for : 数据的遍历
while 和 for 部分代码可以互相转换