blocks|key|1296974|text|__init__需要返回None。您不能(或者至少不应该)返回其他内容。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1296975|尝试创建您想要返回的任何实例变量(或函数)。|1296976|>>>+class+Foo:
...+++++def+__init__(self):
...+++++++++return+42
...+
>>>+foo+=+Foo()
Traceback+(most+recent+call+last):
++File+"<stdin>",+line+1,+in+<module>
TypeError:+__init__()+should+return+None|code-block|syntax|javascript|1296977|entityMap^0|0|8|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|S|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

<code>__init__</code> is required to return None. You cannot (or at least shouldn't) return something else.

Try making whatever you want to return an instance variable (or function).

<pre><code>&gt;&gt;&gt; class Foo:
... def __init__(self):
... return 42
... 
&gt;&gt;&gt; foo = Foo()
Traceback (most recent call last):
 File "&lt;stdin&gt;", line 1, in &lt;module&gt;
TypeError: __init__() should return None
</code></pre>

blocks|key|1082043|text|__init__不返回任何内容，应该始终返回None。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1082044|entityMap^0|0|8|M|4|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

<code>__init__</code> doesn't return anything and should always return <code>None</code>.

blocks|key|1297052|text|你为什么要这么做呢？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1297053|如果您希望在调用类时返回其他对象，请使用__new__()方法：|offset|length|style|CODE|1297054|class+MyClass(object):
++++def+__init__(self):
++++++++print+"never+called+in+this+case"
++++def+__new__(cls):
++++++++return+42

obj+=+MyClass()
print+obj|code-block|syntax|javascript|1297055|entityMap^0|0|K|9|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@$D|Q|E|R|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|S|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Why would you want to do that?

If you want to return some other object when a class is called, then use the <code>__new__()</code> method:

<pre><code>class MyClass(object):
 def __init__(self):
 print "never called in this case"
 def __new__(cls):
 return 42

obj = MyClass()
print obj
</code></pre>

blocks|key|1297137|text|与其他方法和函数一样，在缺省情况下，__init__方法在没有返回语句的情况下返回None，因此您可以按以下任意一种方式编写它：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1297138|class+Foo:
++++def+__init__(self):
++++++++self.value=42

class+Bar:
++++def+__init__(self):
++++++++self.value=42
++++++++return+None|code-block|syntax|javascript|1297139|但是，当然，添加return+None不会给您带来任何好处。|1297140|我不确定你想要什么，但你可能会对其中的一个感兴趣：|1297141|class+Foo:
++++def+__init__(self):
++++++++self.value=42
++++def+__str__(self):
++++++++return+str(self.value)

f=Foo()
print+f.value
print+f|1297142|打印：|1297143|42
42|1297144|entityMap^0|I|8|0|0|8|B|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|13|8|@]|D|@]|E|$]]|$1|O|3|P|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|Q|3|R|5|6|7|15|8|@]|D|@]|E|$]]|$1|S|3|T|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|U|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|V|$]]

The <code>__init__</code> method, like other methods and functions returns None by default in the absence of a return statement, so you can write it like either of these:

<pre><code>class Foo:
 def __init__(self):
 self.value=42

class Bar:
 def __init__(self):
 self.value=42
 return None
</code></pre>

But, of course, adding the <code>return None</code> doesn't buy you anything.

I'm not sure what you are after, but you might be interested in one of these:

<pre><code>class Foo:
 def __init__(self):
 self.value=42
 def __str__(self):
 return str(self.value)

f=Foo()
print f.value
print f
</code></pre>

prints:

<pre><code>42
42
</code></pre>

blocks|key|1082144|text|有问题的问题的示例用法可能如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1082145|class+SampleObject(object):

++++def+__new__(cls,+item):
++++++++if+cls.IsValid(item):
++++++++++++return+super(SampleObject,+cls).__new__(cls)
++++++++else:
++++++++++++return+None

++++def+__init__(self,+item):
++++++++self.InitData(item)+#large+amount+of+data+and+very+complex+calculations

...

ValidObjects+=+[]
for+i+in+data:
++++item+=+SampleObject(i)
++++if+item:+++++++++++++#+in+case+the+i+data+is+valid+for+the+sample+object
++++++++ValidObjects.append(item)|code-block|syntax|javascript|1082146|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Sample Usage of the matter in question can be like:
<pre><code>class SampleObject(object):

 def __new__(cls, item):
 if cls.IsValid(item):
 return super(SampleObject, cls).__new__(cls)
 else:
 return None

 def __init__(self, item):
 self.InitData(item) #large amount of data and very complex calculations

...

ValidObjects = []
for i in data:
 item = SampleObject(i)
 if item: # in case the i data is valid for the sample object
 ValidObjects.append(item)
</code></pre>

blocks|key|1297282|text|我只是想补充一下，您可以在__init__中返回类|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1297283|@property
def+failureException(self):
++++class+MyCustomException(AssertionError):
++++++++def+__init__(self_,+*args,+**kwargs):
++++++++++++***+Your+code+here+***
++++++++++++return+super().__init__(*args,+**kwargs)

++++MyCustomException.__name__+=+AssertionError.__name__
++++return+MyCustomException|code-block|syntax|javascript|1297284|上述方法可帮助您在测试中出现异常时实现特定的操作|1297285|entityMap^0|D|8|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

Just wanted to add, you can return classes in <code>__init__</code>

<pre><code>@property
def failureException(self):
 class MyCustomException(AssertionError):
 def __init__(self_, *args, **kwargs):
 *** Your code here ***
 return super().__init__(*args, **kwargs)

 MyCustomException.__name__ = AssertionError.__name__
 return MyCustomException
</code></pre>

The above method helps you implement a specific action upon an Exception in your test

blocks|key|1082260|text|好吧，如果你不再关心对象实例...你可以直接替换它！|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1082261|class+MuaHaHa():
def+__init__(self,+ret):
++++self=ret

print+MuaHaHa('foo')=='foo'|code-block|syntax|javascript|1082262|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Well, if you don't care about the object instance anymore ... you can just replace it!

<pre><code>class MuaHaHa():
def __init__(self, ret):
 self=ret

print MuaHaHa('foo')=='foo'
</code></pre>

blocks|key|1082312|text|您可以将其设置为一个类变量，然后从主程序中读取它：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1082313|class+Foo:
++++def+__init__(self):
++++++++#Do+your+stuff+here
++++++++self.returncode+=+42
bar+=+Foo()
baz+=+bar.returncode|code-block|syntax|javascript|1082314|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can just set it to a class variable and read it from the main program:

<pre><code>class Foo:
 def __init__(self):
 #Do your stuff here
 self.returncode = 42
bar = Foo()
baz = bar.returncode
</code></pre>

I have a class with an <code>__init__</code> function. 

How can I return an integer value from this function when an object is created?

I wrote a program, where <code>__init__</code> does command line parsing and I need to have some value set. Is it OK set it in global variable and use it in other member functions? If so how to do that? So far, I declared a variable outside class. and setting it one function doesn't reflect in other function ??

How to return a value from __init__ in Python?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个带有__init__函数的类。当创建一个对象时，我如何从这个函数返回一个整数值？我写了一个程序，其中__init__执行命令行解析，我需要设置一些值。是否可以在全局变量中设置它并在其他成员函数中使用它？如果是这样的话，该怎么做呢？到目前为止，我在类外部声明了一个变量。并且设置一个函数不会反映在其他函数中?？

问如何在Python中从init返回值？
EN

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问如何在Python中从__init__返回值？EN