dict理解中的Python作用域 [英] Python scoping in dict comprehension

问题描述

>>> x = 'foo'
>>> {0: locals().get('x')}
{0: 'foo'}
>>> {0: locals().get('x' + spam) for spam in ['']}
{0: None}

这种行为差异的原因是什么?

解决方案

Dict理解和生成器理解会创建自己的局部范围.列表推导在Python 2.x中不是，但在Python 3中却是.(请注意，您的第一个示例不是dict推导.它只是一个文字dict，碰巧有一个表达式作为键0的值.)

>>> x = 'foo'
>>> {0: locals().get('x')}
{0: 'foo'}
>>> {0: locals().get('x' + spam) for spam in ['']}
{0: None}

What is the reason for this discrepancy in behaviour?

解决方案

Dict comprehensions and generator comprehensions create their own local scope. List comprehensions do not in Python 2.x, but do in Python 3. (Note that your first example is not a dict comprehension. It's just a literal dict that happens to have an expression as the value for the key 0.)

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