blocks|key|992069|text|我认为这里的关键是你所说的“访问”是什么意思。在闭包作用域之外读取变量应该没有问题，例如，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|992070|x+=+3
def+outer():
++++def+inner():
++++++++print+x
++++inner()
outer()|code-block|syntax|javascript|992071|应该可以正常工作(打印3)。然而，覆盖x的值不起作用，例如，|992072|x+=+3
def+outer():
++++def+inner():
++++++++x+=+5
++++inner()
outer()
print+x|992073|将仍然打印3。根据我对PEP-3104的理解，这就是非本地关键字要涵盖的内容。正如在PEP中提到的，您可以使用一个类来完成相同的事情(有点混乱)：|offset|length|992074|class+Namespace(object):+pass
ns+=+Namespace()
ns.x+=+3
def+outer():
++++def+inner():
++++++++ns.x+=+5
++++inner()
outer()
print+ns.x|992075|entityMap|0|LINK|mutability|MUTABLE|url|http://www.python.org/dev/peps/pep-3104/^0|0|0|0|0|B|8|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|12|8|@]|9|@$M|13|N|14|1|15]]|A|$]]|$1|O|3|P|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

I think the key here is what you mean by "access". There should be no issue with reading a variable outside of the closure scope, e.g.,

<pre><code>x = 3
def outer():
 def inner():
 print x
 inner()
outer()
</code></pre>

should work as expected (printing 3). However, overriding the value of x does not work, e.g.,

<pre><code>x = 3
def outer():
 def inner():
 x = 5
 inner()
outer()
print x
</code></pre>

will still print 3. From my understanding of <a href="http://www.python.org/dev/peps/pep-3104/" rel="noreferrer">PEP-3104</a> this is what the nonlocal keyword is meant to cover. As mentioned in the PEP, you can use a class to accomplish the same thing (kind of messy):

<pre><code>class Namespace(object): pass
ns = Namespace()
ns.x = 3
def outer():
 def inner():
 ns.x = 5
 inner()
outer()
print ns.x
</code></pre>

blocks|key|992112|text|python的作用域规则中有一个缺点-赋值使变量位于其直接封闭的函数作用域的局部。对于全局变量，可以使用global关键字来解决这个问题。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|992113|解决方案是引入一个在两个作用域之间共享的对象，该对象包含可变变量，但其本身是通过未赋值的变量引用的。|992114|def+outer(v):
++++def+inner(container+=+[v]):
++++++++container[0]+%2B=+1
++++++++return+container[0]
++++return+inner|code-block|syntax|javascript|992115|另一种选择是一些作用域黑客：|992116|def+outer(v):
++++def+inner(varname+=+'v',+scope+=+locals()):
++++++++scope[varname]+%2B=+1
++++++++return+scope[varname]
++++return+inner|992117|您也许能够想出一些技巧来将参数的名称传递给outer，然后将其作为outer传递，但是如果不依赖于名称varname，则需要使用Y组合符。|992118|entityMap^0|1G|6|0|0|0|0|0|L|5|X|5|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|Z|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|T|$]]

There is a wart in python's scoping rules - assignment makes a variable local to its immediately enclosing function scope. For a global variable, you would solve this with the <code>global</code> keyword.

The solution is to introduce an object which is shared between the two scopes, which contains mutable variables, but is itself referenced through a variable which is not assigned. 

<pre><code>def outer(v):
 def inner(container = [v]):
 container[0] += 1
 return container[0]
 return inner
</code></pre>

An alternative is some scopes hackery:

<pre><code>def outer(v):
 def inner(varname = 'v', scope = locals()):
 scope[varname] += 1
 return scope[varname]
 return inner
</code></pre>

You might be able to figure out some trickery to get the name of the parameter to <code>outer</code>, and then pass it as varname, but without relying on the name <code>outer</code> you would like need to use a Y combinator.

blocks|key|1206648|text|在Python2中还有另一种实现非局部变量的方法，以防这里的任何答案因任何原因而不可取：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1206649|def+outer():
++++outer.y+=+0
++++def+inner():
++++++++outer.y+%2B=+1
++++++++return+outer.y
++++return+inner

f+=+outer()
print(f(),+f(),+f())+#prints+1+2+3|code-block|syntax|javascript|1206650|在变量的赋值语句中使用函数名是多余的，但在我看来，这比将变量放在字典中更简单、更干净。从一个调用到另一个调用时会记住该值，就像在Chris+B.的回答中一样。|1206651|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|$]]

There is another way to implement nonlocal variables in Python 2, in case any of the answers here are undesirable for whatever reason:

<pre><code>def outer():
 outer.y = 0
 def inner():
 outer.y += 1
 return outer.y
 return inner

f = outer()
print(f(), f(), f()) #prints 1 2 3
</code></pre>

It is redundant to use the name of the function in the assignment statement of the variable, but it looks simpler and cleaner to me than putting the variable in a dictionary. The value is remembered from one call to another, just like in Chris B.'s answer.

blocks|key|992227|text|下面的解决方案受到answer+by++Elias+Zamaria的启发，但与答案相反的是，它确实正确地处理了外部函数的多次调用。对于当前的outer调用，“变量”inner.y是本地的。只是它不是一个变量，因为这是被禁止的，而是一个对象属性(对象是函数inner本身)。这非常难看(请注意，该属性只能在定义inner函数之后创建)，但似乎很有效。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|992228|def+outer():
++++def+inner():
++++++++inner.y+%2B=+1
++++++++return+inner.y
++++inner.y+=+0
++++return+inner

f+=+outer()
g+=+outer()
print(f(),+f(),+g(),+f(),+g())+#prints+(1,+2,+1,+3,+2)|code-block|syntax|javascript|992229|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/13794589/281545^0|1Y|5|2A|7|3J|5|4A|5|9|O|0|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|@$9|11|A|12|1|13]]|E|$]]|$1|F|3|G|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

The following solution is inspired by the <a href="https://stackoverflow.com/a/13794589/281545">answer by Elias Zamaria</a>, but contrary to that answer does handle multiple calls of the outer function correctly. The "variable" <code>inner.y</code> is local to the current call of <code>outer</code>. Only it isn't a variable, since that is forbidden, but an object attribute (the object being the function <code>inner</code> itself). This is very ugly (note that the attribute can only be created after the <code>inner</code> function is defined) but seems effective.

<pre><code>def outer():
 def inner():
 inner.y += 1
 return inner.y
 inner.y = 0
 return inner

f = outer()
g = outer()
print(f(), f(), g(), f(), g()) #prints (1, 2, 1, 3, 2)
</code></pre>

blocks|key|992262|text|使用全局变量|type|unstyled|depth|inlineStyleRanges|entityRanges|data|992263|def+outer():
++++global+y+#+import1
++++y+=+0
++++def+inner():
++++++++global+y+#+import2+-+requires+import1
++++++++y+%2B=+1
++++++++return+y
++++return+inner

f+=+outer()
print(f(),+f(),+f())+#prints+1+2+3|code-block|syntax|javascript|992264|就我个人而言，我不喜欢全局变量。但是，我的建议是基于https://stackoverflow.com/a/19877437/1083704+answer|offset|length|992265|def+report():
++++++++class+Rank:+
++++++++++++def+__init__(self):
++++++++++++++++report.ranks+%2B=+1
++++++++rank+=+Rank()
report.ranks+=+0
report()|992266|每次需要调用report时，用户都需要声明一个全局变量ranks。我的改进消除了用户初始化函数变量的需要。|style|CODE|992267|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/19877437/1083704^0|0|0|Q|18|0|0|0|6|6|R|5|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@$I|11|J|12|1|13]]|A|$]]|$1|K|3|L|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|15|8|@$I|16|J|17|O|P]|$I|18|J|19|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

Use a global variable

<pre><code>def outer():
 global y # import1
 y = 0
 def inner():
 global y # import2 - requires import1
 y += 1
 return y
 return inner

f = outer()
print(f(), f(), f()) #prints 1 2 3
</code></pre>

Personally, I do not like the global variables. But, my proposal is based on <a href="https://stackoverflow.com/a/19877437/1083704">https://stackoverflow.com/a/19877437/1083704</a> answer

<pre><code>def report():
 class Rank: 
 def __init__(self):
 report.ranks += 1
 rank = Rank()
report.ranks = 0
report()
</code></pre>

where user needs to declare a global variable <code>ranks</code>, every time you need to call the <code>report</code>. My improvement eliminates the need to initialize the function variables from the user.

blocks|key|1206775|text|另一种方法(尽管太过冗长)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1206776|import+ctypes

def+outer():
++++y+=+0
++++def+inner():
++++++++ctypes.pythonapi.PyCell_Set(id(inner.func_closure[0]),+id(y+%2B+1))
++++++++return+y
++++return+inner

x+=+outer()
x()
>>+1
x()
>>+2
y+=+outer()
y()
>>+1
x()
>>+3|code-block|syntax|javascript|1206777|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|$]]

Another way to do it (although it's too verbose):

<pre><code>import ctypes

def outer():
 y = 0
 def inner():
 ctypes.pythonapi.PyCell_Set(id(inner.func_closure[0]), id(y + 1))
 return y
 return inner

x = outer()
x()
&gt;&gt; 1
x()
&gt;&gt; 2
y = outer()
y()
&gt;&gt; 1
x()
&gt;&gt; 3
</code></pre>

blocks|key|1206843|text|这里有一些灵感来自于Alois+Mahdal在comment中关于另一个answer的建议|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1206844|class+Nonlocal(object):
++++"""+Helper+to+implement+nonlocal+names+in+Python+2.x+"""
++++def+__init__(self,+**kwargs):
++++++++self.__dict__.update(kwargs)


def+outer():
++++nl+=+Nonlocal(y=0)
++++def+inner():
++++++++nl.y+%2B=+1
++++++++return+nl.y
++++return+inner

f+=+outer()
print(f(),+f(),+f())+#+->+(1+2+3)|code-block|syntax|javascript|1206845|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/3190706/nonlocal-keyword-in-python-2-x/3190783#comment26766745_3190783|1|https://stackoverflow.com/a/3190783/355230^0|N|7|0|10|6|1|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]|$A|W|B|X|1|Y]]|C|$]]|$1|D|3|E|5|F|7|Z|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]|Q|$5|L|M|N|C|$O|R]]]]

Here's something inspired by a suggestion Alois Mahdal made in a <a href="https://stackoverflow.com/questions/3190706/nonlocal-keyword-in-python-2-x/3190783#comment26766745_3190783">comment</a> regarding another <a href="https://stackoverflow.com/a/3190783/355230">answer</a>:
<pre><code>class Nonlocal(object):
 &quot;&quot;&quot; Helper to implement nonlocal names in Python 2.x &quot;&quot;&quot;
 def __init__(self, **kwargs):
 self.__dict__.update(kwargs)


def outer():
 nl = Nonlocal(y=0)
 def inner():
 nl.y += 1
 return nl.y
 return inner

f = outer()
print(f(), f(), f()) # -&gt; (1 2 3)
</code></pre>

blocks|key|992399|text|将上面的Martineau优雅解决方案扩展到一个实用的用例，但我得到的用例不太优雅：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|992400|class+nonlocals(object):
"""+Helper+to+implement+nonlocal+names+in+Python+2.x.
Usage+example:
def+outer():
+++++nl+=+nonlocals(+n=0,+m=1+)
+++++def+inner():
+++++++++nl.n+%2B=+1
+++++inner()+#+will+increment+nl.n

or...
++++sums+=+nonlocals(+{+k:v+for+k,v+in+locals().iteritems()+if+k.startswith('tot_')+}+)
"""
def+__init__(self,+**kwargs):
++++self.__dict__.update(kwargs)

def+__init__(self,+a_dict):
++++self.__dict__.update(a_dict)|code-block|syntax|javascript|992401|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|$]]

Extending Martineau elegant solution above to a practical and somewhat less elegant use case I get:

<pre><code>class nonlocals(object):
""" Helper to implement nonlocal names in Python 2.x.
Usage example:
def outer():
 nl = nonlocals( n=0, m=1 )
 def inner():
 nl.n += 1
 inner() # will increment nl.n

or...
 sums = nonlocals( { k:v for k,v in locals().iteritems() if k.startswith('tot_') } )
"""
def __init__(self, **kwargs):
 self.__dict__.update(kwargs)

def __init__(self, a_dict):
 self.__dict__.update(a_dict)
</code></pre>

I'm trying to implement a closure in Python 2.6 and I need to access a nonlocal variable but it seems like this keyword is not available in python 2.x. How should one access nonlocal variables in closures in these versions of python?

nonlocal keyword in Python 2.x

Python

我正在尝试在Python2.6中实现一个闭包，并且我需要访问一个非局部变量，但是这个关键字似乎在Python2.x中不可用。在这些版本的python中，应该如何访问闭包中的非局部变量？

问Python 2.x中的非本地关键字
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