用Python冻结吗? [英] Freeze in Python?
问题描述
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,我只是遇到了一个不知道如何在Python中进行复制的Ruby功能.这是Ruby的freeze
方法.
I have programmed in Python for a while, and just recently started using Ruby at work. The languages are very similar. However, I just came across a Ruby feature that I don't know how to replicate in Python. It's Ruby's freeze
method.
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中模仿它?
Is there a way to imitate this in Python?
我意识到我使它看起来似乎只用于列表.在Ruby中,freeze
是Object
上的方法,因此您可以使任何对象不可变.对于造成的困扰,我深表歉意.
I realized that I made it seem like this was only for lists; in Ruby, freeze
is a method on Object
so you can make any object immutable. I apologize for the confusion.
推荐答案
您始终可以将list
子类化,并添加冻结"标志,该标志将阻止__setitem__
做任何事情:
You could always subclass list
and add the "frozen" flag which would block __setitem__
doing anything:
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:
>>> 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
>>>
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