python基础语法--for循环

for循环

语法： for [变量名] in [可迭代对象]: [指令]
例如 字符串遍历：

    name = "Ted"
    for c in name:
        print(c)

输出：
T
e
d

列表遍历：

 name = ["Ted", "Marry", "David"]
    for c in name:
        print(c)
Ted
Marry
David

字典遍历：

 name = {"name1" : "Ted","name2": "Marry","name3": "David"}
    for c in name:
        print(c)
     

输出：
name1
name2
name3
相当于遍历索引元组
如果遍历值：

 for c in name:
        print(name[c])

Ted
Marry
David

通过遍历来修改元素值，以列表为例：

 name = ["Ted", "Marry", "David"]
    i = 0
    for c in name:
        new = name[i]
        name[i] = new.upper()
        i += 1
    print(name)

[‘TED’, ‘MARRY’, ‘DAVID’]
实际上用i作为列表的索引，来进行操作，由于访问可迭代对象中的索引和元素是很常见的操作，python提供了一个专门的语法：

  name = ["Ted", "Marry", "David"]
    for i, c in enumerate(name):
        new = name[i]
        name[i] = new.upper()
    print(name)

上例没有遍历name的列表，而是将其调给了enumerate函数去遍历该函数返回结果。

range函数，总共有三个参数，分别为起始值，结束值，递减大小
例如：

    for i in range(1, 6, 2):
        print(i)

1
3
5