python: 列表、字典

列表的赋值语句不创建拷贝。你得使用切片操作符来建立序列的拷贝。

# Filename: reference.py

print 'Simple Assignment'
shoplist = ['apple', 'mango', 'carrot', 'banana']
mylist = shoplist # mylist is just another name pointing to the same object!

del shoplist[0]

print 'shoplist is', shoplist
print 'mylist is', mylist
# notice that both shoplist and mylist both print the same list without
# the 'apple' confirming that they point to the same object

print 'Copy by making a full slice'
mylist = shoplist[:] # make a copy by doing a full slice
del mylist[0] # remove first item

print 'shoplist is', shoplist
print 'mylist is', mylist
# notice that now the two lists are different

输出：
$ python reference.py
Simple Assignment
shoplist is ['mango', 'carrot', 'banana']
mylist is ['mango', 'carrot', 'banana']
Copy by making a full slice
shoplist is ['mango', 'carrot', 'banana']
mylist is ['carrot', 'banana']

1. 首先给出一个字典对象a：

>>> a = {'a':'a_v','b':'b_v'}

2. 下面对字典进行遍历：

方式1：（错误方式）
>>> for key in a:
	print %(key, a[key])
	
SyntaxError: invalid syntax

方式2：（正确方式）

>>> for key in a:print 'key: %s, value: %s' %(key, a[key])key: a, value: a_vkey: b, value: b_v

3. 解析：
注意：方式1错误是因为缺少了%s这个符号。