[英]Problems with deepcopying sys.stdout in python
I have the following problem with copy.deepcopy. 我在copy.deepcopy中遇到以下问题。 It is to do with deepcopying sys.stdout
与复制sys.stdout有关
import sys, copy
class Example:
def __init__(self, value, outa=sys.stdout):
self.value = value
self.outa = outa
def saying_hello_world(self):
print>>self.outa, "Hello world! My value is ", self.value
example_1 = Example(3)
example_1.saying_hello_world()
example_2 = copy.deepcopy(example_1)
example_2.value = 5
example_2.saying_hello_world()
Leads to error 导致错误
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 6, in saying_hello_world
ValueError: I/O operation on closed file
For various reasons I need to deepcopy (as I change example_2 in various ways in my more complex situation, and so need a deepcopy). 由于各种原因,我需要进行深度复制(因为在更复杂的情况下以各种方式更改example_2,因此需要进行深度复制)。 However, when it deepcopies
sys.stdout
, it transfers it from outputting into thee screen and instead outputs it to a closed file, which then gets the error above. 但是,当它深度复制
sys.stdout
,它会将其从输出转移到屏幕上,而是输出到一个关闭的文件中,然后该文件上面的错误。 An obvious solution to this is 一个明显的解决方案是
example_2 = copy.deepcopy(example_1)
example_2.outa = example_1.outa
Is there a better way around this? 有没有更好的办法解决这个问题? Or a better way of deepcopying?
还是更好的复制方式? Thank you!
谢谢!
You can write your own mechanism for deepcoping object using magicmethod __deepcopy__
您可以使用magicmethod__deepcopy__编写自己的对象深度
__deepcopy__
机制
Here is working example for your code: 这是您的代码的工作示例:
import sys, copy
class Example:
def __init__(self, value, outa=sys.stdout):
self.value = value
self.outa = outa
def saying_hello_world(self):
print>>self.outa, "Hello world! My value is ", self.value
def __deepcopy__(self, memo):
# deepcopy self.value, but pass just a reference of self.outa
return Example(copy.deepcopy(self.value, memo), self.outa)
example_1 = Example(3)
example_1.saying_hello_world()
example_2 = copy.deepcopy(example_1)
example_2.value = 5
example_2.saying_hello_world()
It is not ideal (you'll need care if subclassing this, as deepcopy of child will return instance of parent!) but should give you an idea how to implement this in your real life application. 这不是理想的选择(如果将其子类化,则需要注意,因为child的Deepcopy将返回parent的实例!),但是应该给您一个想法,如何在您的实际应用程序中实现它。
You can customise how your instances are copied, and just share the output if it is sys.stdout
, using the __deepcopy__
method: 您可以自定义实例的复制方式,并使用
__deepcopy__
方法共享输出(如果是sys.stdout
:
class Example:
def __init__(self, value, outa=sys.stdout):
self.value = value
self.outa = outa
def saying_hello_world(self):
print >> self.outa, "Hello world! My value is ", self.value
def __deepcopy__(self, memo):
outa = self.outa if self.outa is sys.stdout else deepcopy(self.outa, memo)
return Example(deepcopy(self.value, memo), outa)
You can adjust the logic for when to copy the outa
attribute; 您可以调整何时复制
outa
属性的逻辑。 perhaps not copying anything that is an open file object is a good idea, for example, or never copying that attribute. 例如,也许不复制打开文件对象的任何内容是个好主意,或者永远不要复制该属性。
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