blocks|key|937225|text|首先，快速浏览一下emulating+numeric+types参考手册中的文档。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|937226|(不要太纠结于此-它只是为了让您熟悉一些Python中的算术运算的基本方法)|937227|然后参考numbers+module的文档，其中包括与模拟不同类型的数字最相关的所有抽象基类(例如，用于自定义整数的numbers.Integral+)。|style|CODE|937228|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/reference/datamodel.html#emulating-numeric-types|1|http://docs.python.org/library/numbers^0|9|N|0|0|0|4|7|1M|G|4|E|1|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]]|C|$]]|$1|D|3|E|5|6|7|X|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|Y|8|@$A|Z|B|10|H|I]|$A|11|B|12|H|I]]|9|@$A|13|B|14|1|15]]|C|$]]|$1|J|3|-4|5|6|7|16|8|@]|9|@]|C|$]]]|K|$L|$5|M|N|O|C|$P|Q]]|R|$5|M|N|O|C|$P|S]]]]

First, take a quick look at the documentation in the reference manual on <a href="http://docs.python.org/reference/datamodel.html#emulating-numeric-types" rel="noreferrer">emulating numeric types</a>.

(Don't get too stuck on that - it's just to give you some familiarity with the methods underlying arithmetic operations in Python)

Then refer to the documentation for the <a href="http://docs.python.org/library/numbers" rel="noreferrer"><code>numbers</code> module</a>, which includes all the Abstract Base Classes that are most relevant to emulating different kinds of numbers (e.g. <code>numbers.Integral</code> for custom integers).

blocks|key|721358|text|您可以使用operator+overloading|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|721359|class+Integer:

++def+__init__(self,+value):
++++self.value+=+value

++def+__repr__(self):
++++return+str(self.value)

++def+__add__(self,+value):
++++self.value+%2B=+value
++++return+self

a+=+Integer(2)
print+a

a+=+a%2B3
print+a

a+%2B=+4
print+a|code-block|syntax|javascript|721360|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/release/1.4/tut/node90.html^0|5|K|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

You can use <a href="http://docs.python.org/release/1.4/tut/node90.html" rel="nofollow">operator overloading</a>:

<pre><code>class Integer:

 def __init__(self, value):
 self.value = value

 def __repr__(self):
 return str(self.value)

 def __add__(self, value):
 self.value += value
 return self

a = Integer(2)
print a

a = a+3
print a

a += 4
print a
</code></pre>

blocks|key|721422|text|我假设你希望你的Integer类是可变的。为了得到你的例子，这将会起作用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|721423|class+Integer(object):
++++def+__init__(self,+num):
++++++++self._val+=+num

++++def+__iadd__(self,+other):
++++++++self._val+%2B=+int(other)

++++def+__str__(self):
++++++++return+str(self._val)|code-block|syntax|javascript|721424|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|$]]

I assume you want your Integer class to be mutable. To get your example, this will work:

<pre><code>class Integer(object):
 def __init__(self, num):
 self._val = num

 def __iadd__(self, other):
 self._val += int(other)

 def __str__(self):
 return str(self._val)
</code></pre>

blocks|key|937272|text|如果你想重载默认类型转换为字符串方法的操作符，你要找的短语是“魔术方法”。这些方法的名称类似于"__<name>__“，在直接方法调用之外的情况下由python使用。您可能希望为您的类定义__add__和__str__方法，以便第2行和第3行分别工作。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|937273|值得一提的是，如果您的新类型是左操作数，则将调用__add__方法，并且任何类型都可以作为其参数传递。当您的操作数是正确的操作数时，还应该定义__radd__方法。这适用于所有的二元运算符。|937274|有关数值类型的魔术方法的更完整列表，请参阅Emulating+Numeric+Types。|937275|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/reference/datamodel.html#emulating-numeric-types^0|1C|A|2M|7|2U|7|0|O|7|1Z|8|0|L|N|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|13|8|@]|D|@$9|14|A|15|1|16]]|E|$]]|$1|J|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]]]

If you want to overload operators of the default cast-to-string method, the phrase you're looking for is "magic methods". These are the methods named like "<code>__&lt;name&gt;__</code>" and are used by python in cases other than direct method calls. You would want to define the <code>__add__</code> and <code>__str__</code> methods for your class in order for lines 2 and 3, respectively, to work.

Its worth mentioning that the <code>__add__</code> method will be called if your new type is the left operand, and any type may be passed as its argument. For cases when yours is the right operand, you should also define the <code>__radd__</code> method. This goes for all of the binary operators.

For a more complete list of magic methods for a numeric type, see <a href="http://docs.python.org/reference/datamodel.html#emulating-numeric-types" rel="nofollow">Emulating Numeric Types</a>.

blocks|key|937291|text|class+Integer(object):

++++def+__init__(self,+value=0):
++++++++self._value+=+int(value)

++++def+__add__(self,+other):
++++++++if+isinstance(other,+Integer):
++++++++++++return+Integer(self._value+%2B+other._value)
++++++++return+Integer(self._value+%2B+other)

++++def+__iadd__(self,+other):
++++++++if+isinstance(other,+Integer):
++++++++++++self._value+%2B=+other._value
++++++++else:
++++++++++++self._value+%2B=+other
++++++++return+self

++++def+__sub__(self,+other):
++++++++if+isinstance(other,+Integer):
++++++++++++return+Integer(self._value+-+other._value)
++++++++return+Integer(self._value+-+other)

++++def+__isub__(self,+other):
++++++++if+isinstance(other,+Integer):
++++++++++++self._value+-=+other._value
++++++++else:
++++++++++++self._value+-=+other
++++++++return+self

++++def+__mul__(self,+other):
++++++++if+isinstance(other,+Integer):
++++++++++++return+Integer(self._value+*+other._value)
++++++++return+Integer(self._value+*+other)

++++def+__div__(self,+other):
++++++++if+isinstance(other,+Integer):
++++++++++++return+Integer(self._value+/+other._value)
++++++++return+Integer(self._value+/+other)

++++def+__str__(self):
++++++++return+str(self._value)

++++def+__int__(self):
++++++++return+self._value

++++def+__float__(self):
++++++++return+float(self._value)

++++def+__repr__(self):
++++++++return+'Integer(%25s)'+%25+self._value|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|937292|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>class Integer(object):

 def __init__(self, value=0):
 self._value = int(value)

 def __add__(self, other):
 if isinstance(other, Integer):
 return Integer(self._value + other._value)
 return Integer(self._value + other)

 def __iadd__(self, other):
 if isinstance(other, Integer):
 self._value += other._value
 else:
 self._value += other
 return self

 def __sub__(self, other):
 if isinstance(other, Integer):
 return Integer(self._value - other._value)
 return Integer(self._value - other)

 def __isub__(self, other):
 if isinstance(other, Integer):
 self._value -= other._value
 else:
 self._value -= other
 return self

 def __mul__(self, other):
 if isinstance(other, Integer):
 return Integer(self._value * other._value)
 return Integer(self._value * other)

 def __div__(self, other):
 if isinstance(other, Integer):
 return Integer(self._value / other._value)
 return Integer(self._value / other)

 def __str__(self):
 return str(self._value)

 def __int__(self):
 return self._value

 def __float__(self):
 return float(self._value)

 def __repr__(self):
 return 'Integer(%s)' % self._value
</code></pre>

blocks|key|937331|text|试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|937332|class+Integer(int):
++++def+__init__(self,+value):
++++++++self.value+=+value
++++#+Add+extra+stuff+here.|code-block|syntax|javascript|937333|这将生成一个基于int的类，该类负责__repr__、__iadd__和__isub__。|offset|length|style|CODE|937334|entityMap^0|0|0|I|8|R|8|10|8|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]|$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|N|$]]

Try this:

<pre><code>class Integer(int):
 def __init__(self, value):
 self.value = value
 # Add extra stuff here.
</code></pre>

This will make a class that is based on int, which takes care of the <code>__repr__</code>, <code>__iadd__</code>, and <code>__isub__</code>.

Essentially I want to be able to do something like:

<pre><code>a = Integer(1)
a += 1
print a
</code></pre>

And of course printing the number two as result. What methods do I need to create to get this behaviour in my Integer class?

Disclaimer: I'm not planning to use this for "real", just curious.

Creating my own "integer" object in Python

Python

从本质上讲，我希望能够做到以下几点：a = Integer(1)a += 1print a当然，打印第二个数字作为结果。我需要创建什么方法才能在我的Integer类中获得这种行为？免责声明:我并不打算用它来“真实”，只是好奇而已。

问在Python中创建我自己的“整数”对象
EN

回答 6

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问在Python中创建我自己的“整数”对象EN

回答 6

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