PyOpenWorm.import_contextualizer module

class PyOpenWorm.import_contextualizer.ImportContextualizer

Bases: object

Interface for classes that ‘contextualize’ an import.

Contextualizing an import means that if an object is defined with the name X in some context, and an import statement is written like this:

import X.a

X will be invoked like this:

a = X(__import__('a'))

On the other hand, for an import statement of this form:

from X.a import A

will cause X to be invoked as:

_temp = X(__import__('a', globals(), locals(), ('A',)), ('A',))
A = _temp.A

and the import statement:

from X.a import A as AA

will cause X to be invoked as:

_temp = X(__import__('a', globals(), locals(), ('A',)), ('A',))
AA = _temp.A

meaning that the contextualizer won’t know what the ‘as’ name is.

For the astute reader, you may notice parallels between the protocol for ImportContextualizer and the __import__ function itself. You may also be wondering why the contextualizer isn’t merely a proxy for __import__. The first reason is that I want the true import to always happen, regardless of what the contextualizer does, so that the semantics of the contextualizer are very clear. The second reason is that requiring a real proxy would require more complexity in the contextualizers to ensure that they are properly handling exceptions, module attributes and the return value of __import__, ensuring that the right __import__ is used, as well as handling the ‘fromlist’ correctly.