Question

我已经用Python编程了一段时间，最近才开始在工作中使用Ruby。语言非常相似。但是，我刚刚遇到了一个Ruby功能，我不知道如何在Python中进行复制。这是Ruby的freeze方法。

irb(main):001:0> a = [1,2,3]
=> [1, 2, 3]
irb(main):002:0> a[1] = 'chicken'
=> "chicken"
irb(main):003:0> a.freeze
=> [1, "chicken", 3]
irb(main):004:0> a[1] = 'tuna'
TypeError: can't modify frozen array
        from (irb):4:in `[]='
        from (irb):4

有没有办法在Python中模仿这个？

编辑：我意识到我觉得这只是用于列表;在Ruby中，freeze是Object上的一个方法，因此您可以使任何对象不可变。我为这种困惑道歉。

Answer 1

>>> a = [1,2,3]
>>> a[1] = 'chicken'
>>> a
[1, 'chicken', 3]
>>> a = tuple(a)
>>> a[1] = 'tuna'
Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
    a[1] = 'tuna'
TypeError: 'tuple' object does not support item assignment

另外，参见set与frozenset，bytearray与bytes。

数字，字符串本身是不可变的：

>>> a = 4
>>> id(a)
505408920
>>> a = 42        # different object
>>> id(a)
505409528

Answer 2

你总是可以继承list并添加“冻结”标志，阻止__setitem__做任何事情：

class freezablelist(list):
    def __init__(self,*args,**kwargs):
        list.__init__(self, *args)
        self.frozen = kwargs.get('frozen', False)

    def __setitem__(self, i, y):
        if self.frozen:
            raise TypeError("can't modify frozen list")
        return list.__setitem__(self, i, y)

    def __setslice__(self, i, j, y):
        if self.frozen:
            raise TypeError("can't modify frozen list")
        return list.__setslice__(self, i, j, y)

    def freeze(self):
        self.frozen = True

    def thaw(self):
        self.frozen = False

然后玩它：

>>> from freeze import freezablelist as fl
>>> a = fl([1,2,3])
>>> a[1] = 'chicken'
>>> a.freeze()
>>> a[1] = 'tuna'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "freeze.py", line 10, in __setitem__
    raise TypeError("can't modify frozen list")
TypeError: can't modify frozen list
>>> a[1:1] = 'tuna'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "freeze.py", line 16, in __setslice__
    raise TypeError("can't modify frozen list")
TypeError: can't modify frozen list
>>>

在Python中冻结？

2 个答案: