Python 列表切片语法的使用没有明显的原因

我偶尔会看到 Python 代码中使用的列表切片语法如下：

newList = oldList[:]

当然，这与以下内容相同：

newList = oldList

或者我错过了什么？

[:] 浅拷贝 http://en.wikipedia.org/wiki/Deep_copy#Shallow_copy列表，制作包含对原始列表成员的引用的列表结构的副本。这意味着对副本的操作不会影响原始的结构。但是，如果您对列表成员执行某些操作，两个列表仍会引用它们，因此如果通过原始成员访问成员，则会显示更新。

A 深拷贝 http://en.wikipedia.org/wiki/Deep_copy#Deep_copy也会复印所有名单成员。

下面的代码片段显示了正在运行的浅拷贝。

# ================================================================
# === ShallowCopy.py =============================================
# ================================================================
#
class Foo:
    def __init__(self, data):
        self._data = data

aa = Foo ('aaa')
bb = Foo ('bbb')

# The initial list has two elements containing 'aaa' and 'bbb'
OldList = [aa,bb]
print OldList[0]._data

# The shallow copy makes a new list pointing to the old elements
NewList = OldList[:]
print NewList[0]._data

# Updating one of the elements through the new list sees the
# change reflected when you access that element through the
# old list.
NewList[0]._data = 'xxx'
print OldList[0]._data

# Updating the new list to point to something new is not reflected
# in the old list.
NewList[0] = Foo ('ccc')
print NewList[0]._data
print OldList[0]._data

在 python shell 中运行它会给出以下记录。我们可以看到 使用旧对象的副本制作列表。其中一个对象可以有 它的状态通过旧列表的引用进行更新，并且更新可以是 当通过旧列表访问对象时看到。最后，改变一个 可以看出新列表中的引用没有反映在旧列表中，因为 新列表现在引用不同的对象。

>>> # ================================================================
... # === ShallowCopy.py =============================================
... # ================================================================
... #
... class Foo:
...     def __init__(self, data):
...         self._data = data
...
>>> aa = Foo ('aaa')
>>> bb = Foo ('bbb')
>>>
>>> # The initial list has two elements containing 'aaa' and 'bbb'
... OldList = [aa,bb]
>>> print OldList[0]._data
aaa
>>>
>>> # The shallow copy makes a new list pointing to the old elements
... NewList = OldList[:]
>>> print NewList[0]._data
aaa
>>>
>>> # Updating one of the elements through the new list sees the
... # change reflected when you access that element through the
... # old list.
... NewList[0]._data = 'xxx'
>>> print OldList[0]._data
xxx
>>>
>>> # Updating the new list to point to something new is not reflected
... # in the old list.
... NewList[0] = Foo ('ccc')
>>> print NewList[0]._data
ccc
>>> print OldList[0]._data
xxx