python基础教程： for 循环用法

分手后的思念是犯贱 2022-10-09 03:14 317阅读 0赞

**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