python基础教程： for 循环用法

1.for … in 循环

循环,遍历,迭代 都是指把容器中的数据一个一个获取出来

lst = [1,2,3,4,5]
i = 0
while i<len(lst):
	print(lst[i])
	i+=1
	
# 无法用while 它的索引下标获取集合其中的值;
setvar = {"a","b","c"}


for .. in .. 应用而生

语法:

for 变量 in 可迭代对象:
	code ...

可迭代对象( 通常用到的是: 容器类型数据 , range对象 , 迭代器 )

2.遍历集合

container = {"taibai","wusir","wuchao","bijiao"}
for i in container:
	print(i)

3.遍历列表

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container = ["taibai","wusir","wuchao","bijiao"]
for i in container:
	print(i)

4.遍历元组

container = ("taibai","wusir","wuchao","bijiao")
for i in container:
	print(i)

5.遍历字符串

container = "有时候你的一个微笑,会改变你的一生"
for i in container:
	print(i)

6.遍历字典

container = {1:"a",2:"b",3:"c"}
for i in container:
	print(i)

7.变量的解包[个数要匹配]

a,b = 1,2
a,b = (1,2)
a,b = [1,2]
#a,b = "567" #字符串有局限性,个数是2个,只能用2个变量收;
#a,b = {"a","b"} 集合有局限性,因为无序;
a,b ={"a":1,"b":2}
print(a,b)

8.遍历等长的二级容器

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lst = [("a","b","c"),["d","e","f"],("q","w","e")]
"""
#方法一
for i in lst:
	for en in i:
		print(en)
"""

for en,line,i in lst:
	print(en,line,i)
#en,line,i ("a","b","c")

9.遍历不等长的二级容器

lst = lst = [("a","b","c"),["d","e"],("q",)]
for i in lst:
	for en in i:
		print(en)

#range 对象
"""
range(start,end,step)
start:开始值
end:结束值
step: 步长
最大值end 取不到的,渠道end这个数之前的那个值
"""

range()作用

res = range(10)
print(res)

1)range当中只有1个值

for i in range(10):
	print(i)

2)range当中二个值的情况

for i in range(5,10):
	print(i)

3)range当中三个值得情况下

for i in range(1,15,2):
	print(i)

4)range倒着打印

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for i in range(9,0,-1):
	print(i)

5）99乘法表for改写

#while
i = 1
while i<=9:
	j = 1
	while j <= i:
		print("%s*%s=%2s"% (i,j,i*j),end=" ")
		j += 1
	print()
	i += 1

# #for
for i in range(1,10):
	for j in range(1,i+1):
		print("%d*%d=%2d " % (i,j,i*j) ,end = "")

	print()

总结:

• while 一般用于复杂的逻辑操作
• for 一般用于数据的遍历