blocks|key|1587093|text|调用python列表上的string将调用内部每个元素的__repr__方法。对于某些项目，__str__和__repr__是相同的。如果您想要该行为，请执行以下操作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1587094|def+__str__(self):
++++...
def+__repr__(self):
++++return+self.__str__()|code-block|syntax|javascript|1587095|entityMap^0|S|8|1A|7|1I|8|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

Calling string on a python list calls the <code>__repr__</code> method on each element inside. For some items, <code>__str__</code> and <code>__repr__</code> are the same. If you want that behavior, do:

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

blocks|key|1587154|text|您可以使用list+comprehension自动生成包含每个项目str()'d的新列表：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1587155|print([str(item)+for+item+in+mylist])|code-block|syntax|javascript|1587156|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/tutorial/datastructures.html#list-comprehensions^0|5|I|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 <a href="http://docs.python.org/tutorial/datastructures.html#list-comprehensions" rel="noreferrer">list comprehension</a> to generate a new list with each item str()'d automatically:

<pre><code>print([str(item) for item in mylist])
</code></pre>

blocks|key|1587206|text|您可以做两件简单的事情，使用map函数或使用理解。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1587207|但这会得到一个字符串列表，而不是一个字符串。因此，您还必须将这些字符串连接在一起。|1587208|s=+",".join(+map(+str,+myList+)+)|code-block|syntax|javascript|1587209|或|1587210|s=+",".join(+[+str(element)+for+element+in+myList+]+)|1587211|然后，您可以打印此复合字符串对象。|1587212|print+'my+list+is+%25s'%25(+s+)|1587213|entityMap^0|E|3|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|11|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|12|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|13|8|@]|D|@]|E|$]]|$1|S|3|T|5|J|7|14|8|@]|D|@]|E|$K|L]]|$1|U|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|V|$]]

Two easy things you can do, use the <code>map</code> function or use a comprehension.

But that gets you a list of strings, not a string. So you also have to join the strings together.

<pre><code>s= ",".join( map( str, myList ) )
</code></pre>

or

<pre><code>s= ",".join( [ str(element) for element in myList ] )
</code></pre>

Then you can print this composite string object.

<pre><code>print 'my list is %s'%( s )
</code></pre>

blocks|key|1587263|text|根据您想要使用该输出的用途，也许__repr__可能更合适：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1587264|import+unittest

class+A(object):
++++def+__init__(self,+val):
++++++++self.val+=+val

++++def+__repr__(self):
++++++++return+repr(self.val)

class+Test(unittest.TestCase):
++++def+testMain(self):
++++++++l+=+[A('a'),+A('b')]
++++++++self.assertEqual(repr(l),+"['a',+'b']")

if+__name__+==+'__main__':
++++unittest.main()|code-block|syntax|javascript|1587265|entityMap^0|G|8|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Depending on what you want to use that output for, perhaps <code>__repr__</code> might be more appropriate:

<pre><code>import unittest

class A(object):
 def __init__(self, val):
 self.val = val

 def __repr__(self):
 return repr(self.val)

class Test(unittest.TestCase):
 def testMain(self):
 l = [A('a'), A('b')]
 self.assertEqual(repr(l), "['a', 'b']")

if __name__ == '__main__':
 unittest.main()
</code></pre>

blocks|key|1587317|text|我同意前面关于使用列表理解来做这件事的回答，但是你当然可以把它隐藏在一个函数后面，如果这是你想要的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1587318|def+is_list(value):
++++if+type(value)+in+(list,+tuple):+return+True
++++return+False

def+list_str(value):
++++if+not+is_list(value):+return+str(value)
++++return+[list_str(v)+for+v+in+value]|code-block|syntax|javascript|1587319|只是为了好玩，我让list_str()递归地str()列表中包含的所有内容。|1587320|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I agree with the previous answer about using list comprehensions to do this, but you could certainly hide that behind a function, if that's what floats your boat.

<pre><code>def is_list(value):
 if type(value) in (list, tuple): return True
 return False

def list_str(value):
 if not is_list(value): return str(value)
 return [list_str(v) for v in value]
</code></pre>

Just for fun, I made list_str() recursively str() everything contained in the list.

blocks|key|1372172|text|像这样的东西？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1372173|a+=+[1,+2+,3]
[str(x)+for+x+in+a]
#+['1',+'2',+'3']|code-block|syntax|javascript|1372174|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|$]]

Something like this?

<pre><code>a = [1, 2 ,3]
[str(x) for x in a]
# ['1', '2', '3']
</code></pre>

blocks|key|1372391|text|这应该足够了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1372392|在打印列表和其他容器类时，将使用__repr__打印包含的元素，因为__repr__用于内部对象表示。如果我们调用：help(object.__repr__)，它将告诉我们：|offset|length|style|CODE|1372393|Help+on+wrapper_descriptor:

__repr__(self,+/)
++++Return+repr(self).|code-block|syntax|javascript|1372394|如果我们调用help(repr)，它将输出：|1372395|Help+on+built-in+function+repr+in+module+builtins:

repr(obj,+/)
++++Return+the+canonical+string+representation+of+the+object.

++++For+many+object+types,+including+most+builtins,+eval(repr(obj))+==+obj.|1372396|如果为对象实现了__str__，但__repr__不是，则repr(obj)将输出默认输出，就像未实现时的print(obj)一样。|1372397|所以唯一的方法就是为你的类实现__repr__。一种可能的方法是：|1372398|class+C:+++++++++++
++++def+__str__(self):
++++++++return+str(f"{self.__class__.__name__}+class+str+")

C.__repr__=C.__str__+++++++
ci+=+C()++++


print(ci)+++++++#C+class+str+
print(str(ci))++#C+class+str+
print(repr(ci))+#C+class+str+|1372399|entityMap^0|0|G|8|Y|8|1M|L|0|0|6|A|0|0|8|7|H|8|T|9|1H|A|0|F|8|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@$D|10|E|11|F|G]|$D|12|E|13|F|G]|$D|14|E|15|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|16|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|17|8|@$D|18|E|19|F|G]]|9|@]|A|$]]|$1|O|3|P|5|J|7|1A|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|1B|8|@$D|1C|E|1D|F|G]|$D|1E|E|1F|F|G]|$D|1G|E|1H|F|G]|$D|1I|E|1J|F|G]]|9|@]|A|$]]|$1|S|3|T|5|6|7|1K|8|@$D|1L|E|1M|F|G]]|9|@]|A|$]]|$1|U|3|V|5|J|7|1N|8|@]|9|@]|A|$K|L]]|$1|W|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]]|X|$]]

This should suffice. 

When printing lists as well as other container classes, the contained elements will be printed using <code>__repr__</code>, because <code>__repr__</code> is meant to be used for internal object representation.
If we call: <code>help(object.__repr__)</code> it will tell us:

<pre><code>Help on wrapper_descriptor:

__repr__(self, /)
 Return repr(self).
</code></pre>

And if we call <code>help(repr)</code> it will output:

<pre><code>Help on built-in function repr in module builtins:

repr(obj, /)
 Return the canonical string representation of the object.

 For many object types, including most builtins, eval(repr(obj)) == obj.
</code></pre>

If <code>__str__</code> is implemented for an object and <code>__repr__</code> is not <code>repr(obj)</code> will output the default output, just like <code>print(obj)</code> when non of these are implemented. 

So the only way is to implement <code>__repr__</code> for your class. One possible way to do that is this:

<pre><code>class C: 
 def __str__(self):
 return str(f"{self.__class__.__name__} class str ")

C.__repr__=C.__str__ 
ci = C() 


print(ci) #C class str 
print(str(ci)) #C class str 
print(repr(ci)) #C class str 
</code></pre>

blocks|key|1587362|text|您得到的输出只是对象的模块名、类名，然后不会覆盖十六进制的内存地址，因为__repr__函数没有被覆盖。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1587363|在使用print时，__str__用于对象的字符串表示。但是，由于您打印的是对象列表，而不是遍历列表来调用每个项目的str方法，所以它会打印出对象表示。|1587364|要调用__str__函数，您需要执行以下操作：|1587365|'my+list+is+%25s'+%25+[str(x)+for+x+in+myList]|code-block|syntax|javascript|1587366|如果覆盖__repr__函数，则可以像以前一样使用print方法：|1587367|class+cell:
++++def+__init__(self,+id):
++++++++self.id+=+id
++++def+__str__(self):
++++++++return+str(self.id)+#+Or+whatever
++++def+__repr__(self):
++++++++return+str(self)+#+function+invoked+when+you+try+and+print+the+whole+list.

myList+=+[cell(1),+cell(2),+cell(3)]
'my+list+is+%25s'+%25+myList|1587368|然后你会得到"my+list+is+[1,+2,+3]“作为你的输出。|1587369|entityMap^0|10|8|0|A|7|1M|3|0|3|7|0|0|4|8|0|0|7|K|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|17|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|18|8|@$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|L|7|1B|8|@]|D|@]|E|$M|N]]|$1|S|3|T|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]]|V|$]]

The output you're getting is just the object's module name, class name, and then the memory address in hexadecimal as the the <code>__repr__</code> function is not overridden.

<code>__str__</code> is used for the string representation of an object when using print. But since you are printing a list of objects, and not iterating over the list to call the <code>str</code> method for each item it prints out the objects representation. 

To have the <code>__str__</code> function invoked you'd need to do something like this:

<pre><code>'my list is %s' % [str(x) for x in myList]
</code></pre>

If you override the <code>__repr__</code> function you can use the print method like you were before:

<pre><code>class cell:
 def __init__(self, id):
 self.id = id
 def __str__(self):
 return str(self.id) # Or whatever
 def __repr__(self):
 return str(self) # function invoked when you try and print the whole list.

myList = [cell(1), cell(2), cell(3)]
'my list is %s' % myList
</code></pre>

Then you'll get "<code>my list is [1, 2, 3]</code>" as your output.

In Java, if I call <code>List.toString()</code>, it will automatically call the <code>toString()</code> method on each object inside the List. For example, if my list contains objects <code>o1</code>, <code>o2</code>, and <code>o3</code>, <code>list.toString()</code> would look something like this:
<pre><code>&quot;[&quot; + o1.toString() + &quot;, &quot; + o2.toString() + &quot;, &quot; + o3.toString() + &quot;]&quot;
</code></pre>
Is there a way to get similar behavior in Python? I implemented a <code>__str__()</code> method in my class, but when I print out a list of objects, using:
<pre><code>print 'my list is %s'%(list)
</code></pre>
it looks something like this:
<pre><code>[&lt;__main__.cell instance at 0x2a955e95f0&gt;, &lt;__main__.cell instance at 0x2a955e9638&gt;, &lt;__main__.cell instance at 0x2a955e9680&gt;]
</code></pre>
how can I get python to call my <code>__str__()</code> automatically for each element inside the list (or dict for that matter)?

Python __str__ and lists

容器

Python

Java

在Java语言中，如果我调用List.toString()，它将自动对列表中的每个对象调用toString()方法。例如，如果我的列表包含对象o1、o2和o3，则list.toString()将如下所示："[" + o1.toString() + ", " + o2.toString() + ", " + o3.toString() + "]"有没有办法在Python中获得类似的行为？我在我的类中

问Python str和列表
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回答 8

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