嵌套理解中的NameError [英] NameError in nested comprehensions

问题描述

我在文件中有此代码

class Sudoku(dict):
    COLUMNS = [
        {(x, y) for y in xrange(9)} for x in xrange(9)
    ]

当我运行python broken.py时，我得到了回溯:

When I run python broken.py, I get the traceback:

Traceback (most recent call last):
  File "U:\broken.py", line 1, in <module>
    class Sudoku(dict):
  File "U:\broken.py", line 3, in Sudoku
    {(x, y) for y in xrange(9)} for x in xrange(9)
  File "U:\broken.py", line 3, in <setcomp>
    {(x, y) for y in xrange(9)} for x in xrange(9)
NameError: global name 'x' is not defined
[Finished in 0.1s with exit code 1]

我真的没有在这里看到问题. x不是在理解中定义的吗?

I don't really see the problem here. Isn't x defined in the comprehension?

奇怪的是，当直接粘贴到python解释器中时，它似乎如何执行而没有错误...

What's stranger is how this seems to execute without an error when pasted directly into the python interpreter...

编辑:如果我使用列表推导而不是集合推导，则此方法有效

EDIT: This works if I use a list comprehension rather than a set comprehension

推荐答案

我在此处.在python 2.7.5中，这是仍然被破坏的.

I've filed a bug here. This is still broken by design in python 2.7.5.

来自错误报告:

在Python 2中，列表推导式没有自己的作用域，因此初始示例中的x位于类作用域内.但是，集合理解确实具有其自身的范围.根据设计，在类范围内定义的变量对该类内部的内部范围不可见.

In Python 2, list comprehensions don't have their own scope, so the x in your initial example lives at class scope. However, the set comprehension does have its own scope. By design, a variable defined at class scope is not visible to inner scopes inside that class.

在Python 3中，这是有效的，因为列表理解具有其自身的范围.

In Python 3, this works because the list comprehension has its own scope.

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