Python程序中for循环用法详解
一个通用的序列迭代器，用于遍历任何有序的序列对象内的元素，可用于字符串、元组、列表和其它内置可迭代对象，以及通过类所创建的新对象。
1、for循环语法格式：
for expression in object:
else:
2、for语法格式扩展：
for expression in object:
else:
3、用法示例：
例1：for循环基本用法示例
In [1]: url = 'web2.field.com'
In [2]: for x in url:
w e b 2 . f i e l d . c o m
In [3]: l1 = [1,2,3,4]
In [4]: for i in l1:
1 2 3 4
例2：for-else用法示例
In [5]: for x in url:
else:
w e b 2 . f i e l d . c o m
Game Over!
例2：for-if-else-else用法示例
In [19]: for i in l1:
1
i != 3
2
i != 3
3
i = 3
4
i != 3
Show End
4、for循环练习
练习1：逐一分开显示指定字典d1中的所有元素
In [214]: print d1
{0: 'Sun', 1: 'Mon', 2: 'Tue', 3: 'Wed', 4:'Thu', 5: 'Fri', 6: 'Sat'}
In [215]: d1.items()
Out[215]:
[(0, 'Sun'),
In [216]: for (k,v) in d1.items():
0 Sun
1 Mon
2 Tue
3 Wed
4 Thu
5 Fri
6 Sat
练习2：逐一显示列表中l1=["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]中的索引为奇数的元素；
In [219]: l1=["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]
In [220]: range(1,10,2)
Out[220]: [1, 3, 5, 7, 9]
In [221]: for i in range(1,len(l1),2):
Mon
Wed
Fri
练习3：将属于列表l1=["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]，但不属于列表l2=["Sun","Mon","Tue","Thu","Sat"]的所有元素定义为一个新列表l3;
In [225]:l2=["Sun","Mon","Tue","Thu","Sat"]
In [226]:l2=["Sun","Mon","Tue","Thu","Sat"]
In [227]: for i in l1:
In [228]: print l3
['Wed', 'Fri']
练习4：已知列表namelist=['stu1','stu2','stu3','stu4','stu5','stu6','stu7']，删除列表removelist=['stu3', 'stu7', 'stu9']；请将属于removelist列表中的每个元素从namelist中移除（属于removelist，但不属于namelist的忽略即可)；
In [229]: namelist=['stu1','stu2','stu3','stu4','stu5','stu6','stu7']
In [230]: removelist=['stu3', 'stu7','stu9']
In [231]: for i in namelist:
In [232]: print namelist
['stu2', 'stu4', 'stu6']
练习5、自定义整数列表，修改列表，令列表中每个元素加1
In [235]: l1 = [3,4,56,8,2,9]
In [236]: for i in range(len(l1)):
In [237]: print l1
[4, 5, 57, 9, 3, 10]
练习6：l1 = [1,2,3,4,5,6,7];l2 = ["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]，构造字典d1= {...}
In [238]: l1 = [1,2,3,4,5,6,7];l2 =["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]
In [239]: zip(l1,l2)
Out[239]:
[(1, 'Sun'),
In [240]: for (k,v) in zip(l1,l2):
In [241]: print d1
{0: 'Sun', 1: 'Sun', 2: 'Mon', 3: 'Tue', 4:'Wed', 5: 'Thu', 6: 'Fri', 7: 'Sat'}