blocks|key|795541|text|class+foo(object):
++++def+__str__(self):
++++++++return+"representation"
++++def+__unicode__(self):
++++++++return+u"representation"|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|795542|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 foo(object):
 def __str__(self):
 return "representation"
 def __unicode__(self):
 return u"representation"
</code></pre>

blocks|key|1010173|text|在类的元类中实现__str__()或__repr__()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1010174|class+MC(type):
++def+__repr__(self):
++++return+'Wahaha!'

class+C(object):
++__metaclass__+=+MC

print(C)|code-block|syntax|javascript|1010175|如果你指的是一种可读的字符串化，请使用__str__，对于明确的表示使用__repr__。|1010176|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.python.org/3/reference/datamodel.html#object.__str__|1|https://docs.python.org/3/reference/datamodel.html#object.__repr__^0|8|9|I|A|8|9|0|I|A|1|0|0|J|7|10|8|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@$9|11|A|12|1|13]|$9|14|A|15|1|16]]|E|$]]|$1|F|3|G|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|18|8|@$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]]]

Implement <a href="https://docs.python.org/3/reference/datamodel.html#object.__str__" rel="nofollow noreferrer"><code>__str__()</code></a> or <a href="https://docs.python.org/3/reference/datamodel.html#object.__repr__" rel="nofollow noreferrer"><code>__repr__()</code></a> in the class's metaclass.
<pre><code>class MC(type):
 def __repr__(self):
 return 'Wahaha!'

class C(object):
 __metaclass__ = MC

print(C)
</code></pre>
Use <code>__str__</code> if you mean a readable stringification, use <code>__repr__</code> for unambiguous representations.

blocks|key|1010202|text|如果必须在__repr__或__str__之间进行选择，请选择第一个，因为在默认情况下，实现__str__会在未定义__repr__时调用它。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1010203|自定义Vector3示例：|1010204|class+Vector3(object):
++++def+__init__(self,+args):
++++++++self.x+=+args[0]
++++++++self.y+=+args[1]
++++++++self.z+=+args[2]

++++def+__repr__(self):
++++++++return+"Vector3([{0},{1},{2}])".format(self.x,+self.y,+self.z)

++++def+__str__(self):
++++++++return+"x:+{0},+y:+{1},+z:+{2}".format(self.x,+self.y,+self.z)|code-block|syntax|javascript|1010205|在本例中，repr再次返回一个可以直接使用/执行的字符串，而str更适合作为调试输出。|1010206|v+=+Vector3([1,2,3])
print+repr(v)++++#Vector3([1,2,3])
print+str(v)+++++#x:1,+y:2,+z:3|1010207|entityMap^0|5|8|E|7|1A|7|1M|8|0|0|0|5|4|U|3|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|12|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@]|E|$]]|$1|O|3|P|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|R|$]]

If you have to choose between <code>__repr__</code> or <code>__str__</code> go for the first one, as by default implementation <code>__str__</code> calls <code>__repr__</code> when it wasn't defined. 

Custom Vector3 example:

<pre><code>class Vector3(object):
 def __init__(self, args):
 self.x = args[0]
 self.y = args[1]
 self.z = args[2]

 def __repr__(self):
 return "Vector3([{0},{1},{2}])".format(self.x, self.y, self.z)

 def __str__(self):
 return "x: {0}, y: {1}, z: {2}".format(self.x, self.y, self.z)
</code></pre>

In this example, <code>repr</code> returns again a string that can be directly consumed/executed, whereas <code>str</code> is more useful as a debug output. 

<pre><code>v = Vector3([1,2,3])
print repr(v) #Vector3([1,2,3])
print str(v) #x:1, y:2, z:3
</code></pre>

blocks|key|1010256|text|Ignacio+Vazquez-Abrams'+approved+answer是非常正确的。但是，它来自Python+2代。现在最新的Python+3的更新是：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1010257|class+MC(type):
++def+__repr__(self):
++++return+'Wahaha!'

class+C(object,+metaclass=MC):
++++pass

print(C)|code-block|syntax|javascript|1010258|如果您想要运行在Python2和Python3上的代码，可以使用six模块：|1010259|from+__future__+import+print_function
from+six+import+with_metaclass

class+MC(type):
++def+__repr__(self):
++++return+'Wahaha!'

class+C(with_metaclass(MC)):
++++pass

print(C)|1010260|最后，如果你有一个类，你想要有一个自定义的静态repr，上面基于类的方法效果很好。但是如果有多个，就必须为每个都生成一个类似于MC的元类，这可能会很麻烦。在这种情况下，让元编程更进一步，并创建一个元类工厂会让事情变得更清晰：|style|CODE|1010261|from+__future__+import+print_function
from+six+import+with_metaclass

def+custom_class_repr(name):
++++"""
++++Factory+that+returns+custom+metaclass+with+a+class+``__repr__``+that
++++returns+``name``.
++++"""
++++return+type('whatever',+(type,),+{'__repr__':+lambda+self:+name})

class+C(with_metaclass(custom_class_repr('Wahaha!'))):+pass

class+D(with_metaclass(custom_class_repr('Booyah!'))):+pass

class+E(with_metaclass(custom_class_repr('Gotcha!'))):+pass

print(C,+D,+E)|1010262|打印：|1010263|Wahaha!+Booyah!+Gotcha!|1010264|元编程并不是你通常每天都需要的东西--但当你需要它的时候，它确实切中要害！|1010265|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/4932473/240490|1|https://pypi.org/project/six/^0|0|13|0|0|0|W|3|1|0|0|1R|2|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@$A|19|B|1A|1|1B]]|C|$]]|$1|D|3|E|5|F|7|1C|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|1D|8|@]|9|@$A|1E|B|1F|1|1G]]|C|$]]|$1|K|3|L|5|F|7|1H|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|1I|8|@$A|1J|B|1K|O|P]]|9|@]|C|$]]|$1|Q|3|R|5|F|7|1L|8|@]|9|@]|C|$G|H]]|$1|S|3|T|5|6|7|1M|8|@]|9|@]|C|$]]|$1|U|3|V|5|F|7|1N|8|@]|9|@]|C|$G|H]]|$1|W|3|X|5|6|7|1O|8|@]|9|@]|C|$]]|$1|Y|3|-4|5|6|7|1P|8|@]|9|@]|C|$]]]|Z|$10|$5|11|12|13|C|$14|15]]|16|$5|11|12|13|C|$14|17]]]]

<a href="https://stackoverflow.com/a/4932473/240490">Ignacio Vazquez-Abrams' approved answer</a> is quite right. It is, however, from the Python 2 generation. An update for the now-current Python 3 would be:

 

<pre class="lang-py prettyprint-override"><code>class MC(type):
 def __repr__(self):
 return 'Wahaha!'

class C(object, metaclass=MC):
 pass

print(C)
</code></pre>

If you want code that runs across both Python 2 and Python 3, the <a href="https://pypi.org/project/six/" rel="noreferrer">six</a> module has you covered:

<pre class="lang-py prettyprint-override"><code>from __future__ import print_function
from six import with_metaclass

class MC(type):
 def __repr__(self):
 return 'Wahaha!'

class C(with_metaclass(MC)):
 pass

print(C)
</code></pre>

Finally, if you have one class that you want to have a custom static repr, the class-based approach above works great. But if you have several, you'd have to generate a metaclass similar to <code>MC</code> for each, and that can get tiresome. In that case, taking your metaprogramming one step further and creating a metaclass factory makes things a bit cleaner:

<pre class="lang-py prettyprint-override"><code>from __future__ import print_function
from six import with_metaclass

def custom_class_repr(name):
 """
 Factory that returns custom metaclass with a class ``__repr__`` that
 returns ``name``.
 """
 return type('whatever', (type,), {'__repr__': lambda self: name})

class C(with_metaclass(custom_class_repr('Wahaha!'))): pass

class D(with_metaclass(custom_class_repr('Booyah!'))): pass

class E(with_metaclass(custom_class_repr('Gotcha!'))): pass

print(C, D, E)
</code></pre>

prints:

<pre class="lang-none prettyprint-override"><code>Wahaha! Booyah! Gotcha!
</code></pre>

Metaprogramming isn't something you generally need everyday&mdash;but when you need it, it really hits the spot!

Consider this class:

<pre><code>class foo(object):
 pass
</code></pre>

The default string representation looks something like this:

<pre><code>&gt;&gt;&gt; str(foo)
"&lt;class '__main__.foo'&gt;"
</code></pre>

How can I make this display a custom string?

How to create a custom string representation for a class object?

Python

考虑这个类：class foo(object): pass默认的字符串表示如下所示：>>> str(foo)"<class '__main__.foo'>"如何才能使其显示为自定义字符串？

问如何为类对象创建自定义字符串表示？
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