标签：字典 mil style ict span list bsp div import
1. 列表和字典，直接赋值，都是浅拷贝，即赋值双方指向同一地址，因为 Python 对可变对象按引用传递。
>>> a = [1, 2, 3] >>> b = a >>> b [1, 2, 3] >>> a[0] = ‘apple‘ >>> a [‘apple‘, 2, 3] >>> b [‘apple‘, 2, 3] >>> >>> >>> dic = {‘a‘: ‘apple‘, ‘b‘: ‘banbana‘} >>> dic2 = dic >>> dic2 {‘a‘: ‘apple‘, ‘b‘: ‘banbana‘} >>> dic[‘b‘] = ‘blueberry‘ >>> dic {‘a‘: ‘apple‘, ‘b‘: ‘blueberry‘} >>> dic2 {‘a‘: ‘apple‘, ‘b‘: ‘blueberry‘}
2. 对非嵌套的列表，使用完全切片[:]， 工厂函数 list()，或者 copy.copy() 都是深拷贝。
>>> a = [1, 2, 3] >>> b = list(a) >>> c = a[:] >>> import copy >>> d = copy.copy(a) >>> >>> a[0] = ‘apple‘ >>> a [‘apple‘, 2, 3] >>> b [1, 2, 3] >>> c [1, 2, 3] >>> d [1, 2, 3]
3. 对于非嵌套的字典，使用工厂函数 dict()，或者 copy.copy() 都是深拷贝。
>>> dic = {‘a‘: ‘apple‘, ‘b‘: ‘banana‘}
>>> dic2 = dict(dic)
>>> import copy
>>> dic3 = copy.copy(dic)
>>>
>>> dic[‘b‘] = ‘blueberry‘
>>> dic
{‘a‘: ‘apple‘, ‘b‘: ‘blueberry‘}
>>> dic2
{‘a‘: ‘apple‘, ‘b‘: ‘banana‘}
>>> dic3
{‘a‘: ‘apple‘, ‘b‘: ‘banana‘}
4. 对于嵌套的列表，嵌套的字典，只能使用 copy.deepcopy() 实现深拷贝。
>>> import copy >>> >>> a = [1, 2, [‘apple‘]] >>> b = copy.deepcopy(a) >>> a[2][0] = ‘watermelon‘ >>> a [1, 2, [‘watermelon‘]] >>> b [1, 2, [‘apple‘]] >>> >>> >>> dic = {‘a‘: ‘apple‘, ‘b‘: {‘b1‘: ‘banana‘, ‘b2‘: ‘blueberry‘}} >>> dic2 = copy.deepcopy(dic) >>> dic[‘b‘][‘b1‘] = ‘bukeneng‘ >>> dic {‘a‘: ‘apple‘, ‘b‘: {‘b1‘: ‘bukeneng‘, ‘b2‘: ‘blueberry‘}} >>> dic2 {‘a‘: ‘apple‘, ‘b‘: {‘b1‘: ‘banana‘, ‘b2‘: ‘blueberry‘}}
5. 对于嵌套可变对象的元组，只有 copy.deepcopy() 实现深拷贝。
>>> import copy
>>> >>> t = (1, 2, [‘apple‘]) >>> t2 = t >>> t3 = tuple(t) >>> t4 = copy.copy(t) >>> t5 = copy.deepcopy(t) >>> >>> t[2][0] = ‘watermelon‘ >>> t (1, 2, [‘watermelon‘]) >>> t2 (1, 2, [‘watermelon‘]) >>> t3 (1, 2, [‘watermelon‘]) >>> t4 (1, 2, [‘watermelon‘]) >>> t5 (1, 2, [‘apple‘])
完。
标签：字典 mil style ict span list bsp div import
原文地址：http://www.cnblogs.com/gaowengang/p/7855941.html
