Python中for循环是一个通用的序列迭代器：它可以遍历任何有序序列和其他可迭代对象内的元素。for循环可用于字符串，列表，元组或其他内置可迭代对象。

其语法形式如下：

"""
当运行for循环时，会逐个将可迭代对象object中的元素赋值给target，
然后为每个元素执行循环主体。
"""
 
for target in object:  # 
	statements1 
	if test:
		break       # 跳出循环
	if test:
		continue    # 结束本次循环
else:
	statements2     # 上面没有执行break语句，就会执行到这里

1：简单应用

# 字符串
s = 'ixusy88' 
for x in s:
	print(x)
 
# 列表
lst = ['123','abc','456']
for x in lst:
	print(x)
 
 
"""
输出：
123
abc
456
"""


# 元组
st = ('123','abc','456')
for x in st:
	print(x)

"""
输出：
123
abc
456
"""

2：for循环中的元组赋值

# 1:
lst = [(1,2),(3,4),(5,6)]
for t in lst:
	a,b = t
	print(a,b)
"""
输出
1 2
3 4
5 6
"""
 
for (a,b) in lst:
	print(a,b)
 
"""
输出
1 2
3 4
5 6
"""
#2:
lst = [((1,2),3),((4,5),6)]
for t in lst:
	print(t)
	(a,b),c = t
	print(a,b,c)
 
"""
输出:
((1, 2), 3)
1 2 3
((4, 5), 6)
4 5 6
"""
 
lst = [((1,2),3),((4,5),6)]
for ((a,b),c) in lst:
	print(a,b,c)
"""
输出：
1 2 3
4 5 6
"""
 
# 3:字典：
dic = {'name':'ixusy88','age':18}
for key in dic:
	print(key,'-->',dic[key])
 
"""
输出：
name --> ixusy88
age --> 18
"""
 
dic = {'name':'ixusy88','age':18}
for k,v in dic.items():
	print(k,'-->',v)
 
"""
name --> ixusy88
age --> 18
"""

3：计数器循环：range

"""
print(help(range))
class range(object)
 |  range(stop) -> range object
 |  range(start, stop[, step]) -> range object
    ........
"""
# 0到9
for x in range(10):
	print(x,end=',')
print('')
 
# 输出 0,1,2,3,4,5,6,7,8,9,
 
# 1到9
for x in range(1,10):
	print(x,end=',')
print('')
# 输出 1,2,3,4,5,6,7,8,9,
 
# 1到9，间隔为2
for x in range(1,10,2):
	print(x,end=',')
print('')
# 输出 1,3,5,7,9,
 
 
# 1到9，间隔为3
for x in range(1,10,3):
	print(x,end=',')
print('')
# 输出 1,4,7,

4：偏移量和元素：enumerate

print('--字符串-1-：',)
# 字符串
s = 'ixusy88' 
for x in s:
	print(x)
 
print('--字符串-2-：',)
# 带偏移量
for i,x in enumerate(s):
	print(i,x)
 
print('--列表-1-：',)
# 列表
lst = ['123','abc','456']
for x in lst:
	print(x)
 
print('--列表-2-：',)
for i,x in enumerate(lst):
	print(i,x)
 
print('--元组-1-：',)
# 元组
st = ('123','abc','456')
for x in st:
	print(x)
 
print('--元组-2-：',)
for i,x in enumerate(st):
	print(i,x)

4：推导

# 推导
# 列表推导
t = [x**x for x in range(5)]
print(t)
 
# 集合
t = {x**x for x in range(5)}
print(t)
 
# 字典
t = {x:x**x for x in range(5)}
print(t)

"""
[1, 1, 4, 27, 256]
{256, 1, 27, 4}
{0: 1, 1: 1, 2: 4, 3: 27, 4: 256}
"""