python学习笔记.4使用列表的一部分，创建切片

>>> squares
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
>>> print(squares[0:3])

[1, 4, 9]
如果你没有指定第一个索引，Python将自动从列表开头开始

>>> print(squares[:3])
[1, 4, 9]

要让切片终止于列表末尾，可使用类似的语法

>>> print(squares[2:])
[9, 16, 25, 36, 49, 64, 81, 100]

*负数索引还可以返回离列表末尾相应距离的元素，你可以输出列表末尾的任何切片

>>> print(squares[-3:])
[64, 81, 100]

遍历切片

#helloword.py
numbers=range(1,10)
for number in numbers[:3]:
   print(number)
输出为：
D:\www>python helloword.py
1
2
3

eg:

#helloword.py
my_foods=['egg','banana','cake']
friend_foods=my_foods[:]
my_foods.append('apple')
print('my favorite foods are:')
print(my_foods)
friend_foods.append('pizza')
print('friend favorite foods are:')
print(friend_foods)

输出为：

D:\www>python helloword.py
my favorite foods are:
['egg', 'banana', 'cake', 'apple']
friend favorite foods are:
['egg', 'banana', 'cake', 'pizza']

*倘若我们只是简单的将my_foods赋值给friend_foods,将不能得到两个列表

#helloword.py
my_foods=['egg','banana','cake']
friend_foods=my_foods
my_foods.append('apple')
print('my favorite foods are:')
print(my_foods)
friend_foods.append('pizza')
print('friend favorite foods are:')
print(friend_foods)

输出结果为：

D:\www>python helloword.py
my favorite foods are:
['egg', 'banana', 'cake', 'apple']
friend favorite foods are:
['egg', 'banana', 'cake', 'apple', 'pizza']