意外范围行为的文档

Question

我今天遇到了一个最初让我感到惊讶的范围界定问题。可以通过以下方式轻松证明：

def scope():
    x = 1
    def working():
        print x
    def broken():
        import pdb; pdb.set_trace()
    working()
    broken()


Python 2.7.12 (default, Jul  1 2016, 15:12:24)
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
...
>>> scope()
1
--Return--
> <stdin>(6)broken()->None
(Pdb) x
*** NameError: name 'x' is not defined

Python 3.5.2 (default, Sep 10 2016, 08:21:44)
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> def scope():
...
>>> scope()
1
--Return--
> <stdin>(6)broken()->None
(Pdb) x
*** NameError: name 'x' is not defined
(Pdb)

因此，如果在编译时明确引用了外部范围值，则范围似乎只会包含外部范围值。这肯定是在查看字节码时似乎发生的事情：

  6           0 LOAD_GLOBAL              0 (x)
              3 PRINT_ITEM          
              4 PRINT_NEWLINE       
              5 LOAD_CONST               0 (None)
              8 RETURN_VALUE

这是 Python 如何通过检查绑定函数来区分外部和内部范围引用的产物吗？

Python scoping rules似乎无法解释：

Although scopes are determined statically, they are used dynamically. At any time during execution, there are at least three nested scopes whose namespaces are directly accessible:

the innermost scope, which is searched first, contains the local names

the scopes of any enclosing functions, which are searched starting with the nearest enclosing scope, contains non-local, but also non-global names

我想了解的是上面突出显示的两个部分之间的冲突：作用域是静态的，但似乎并没有兑现可访问名称的承诺。

具体来说，我要查找的是此显式行为的官方文档。

Answer 1

x 不是 broken 的局部变量（"local" 表示在函数内部赋值），因此它不会出现在 locals() 中。

但是，如果对象没有被本地覆盖，您可以从外部范围访问对象，因此您可以在 working.

中访问它

Answer 2

我认为介绍 PEP227（对于 python 2.1！）涵盖了其工作原理的规范。关键部分：

The Python 2.0 definition specifies exactly three namespaces ... the local namespace, the global namespace, and the builtin namespace. According to this definition, if a function A is defined within a function B, the names bound in B are not visible in A. The proposal changes the rules so that names bound in B are visible in A (unless A contains a name binding that hides the binding in B).

...

If a name is used within* a code block, but it is not bound there and is not declared global, the use is treated as a reference to the nearest enclosing function region.

...

An analogous function [to locals() and globals()] will not be provided for nested scopes. Under this proposal, it will not be possible to gain dictionary-style access to all visible scopes.

* 强调位是关键位：您的变量尚未在代码块中使用，因此没有任何内容可以视为对封闭函数的引用。

此外，pdb是动态的运行，当没有指定命令时default (source code link)动作使用exec与locals和globals 从框架。因此，它唯一可用的变量是被检查帧的 locals() 和 globals()，如前所述，它不包括从封闭帧捕获的变量。

意外范围行为的文档

Documentation for unexpected scope behaviour

python

documentation

scope