比while条件循环, 更适合循环取值

names = ["egon", "felix", "richard", "tom", "jack"]
count = 0
while count < len(names):
    print(names[count])
    count += 1

效果等同如下

names = ["egon", "felix", "richard", "tom", "jack"]
for x in names:
    print(x)

for循环还可用于字典和字符串

dic = {"k1": 111, "k2": 222, "k3": 333}
for x in dic:
    print(x, dic[x])

for x in "hello":
    print(x)

for+range控制循环次数

range(1,5)=>[1, 2, 3, 4]
range(5)=>[0, 1, 2, 3, 4]

for x in range(0, 5, 1):
    print("hello")

for 解压赋值

info = [["name", "felix"], ["age", 30]]
for x, y in info:
    print(x, y)

for 循环嵌套, 外层循环一次, 内层全部循环完才跳出

for i in range(3):
    print("======>loop%s" %i)
    for j in range(5):
        print("inner loop%s" %j)