Commits on Feb 17, 2024

1. Replace factory functions with classes. …

   Until now, Element and ElementTree were factory functions.
   Element() returned an _Element class and
   ElementTree() returned an _ElementTree class.
   
   This PR turns them into classes. These classes should behave exactly the same
   as the factory function. Specifically, in both cases:
   
   >>> element = Element("test")
   >>> type(element)
   <class 'lxml.etree._Element'>
   >>> callable(Element)
   True
   
   The difference is that before this change we could not use isinstance:
   
   >>> isinstance(element, etree.Element)
   TypeError: isinstance() arg 2 must be a type, a tuple of types, or a union
   
   While now:
   
   >>> isinstance(element, etree.Element)
   True
   >>> issubclass(_Element, Element)
   True
   
   These checks work because _Element is registered as a virtual subclass of Element.
   
   The motivation for this PR is to support type annotations.
   
   Currently, type stubs for lxml need to annotate the factory functions like this:
   
   def Element(...) -> _Element: ...
   
   Furthermore, the _Element class members are all annotated.
   But _Element was supposed to be kept as an internal implementation.
   
   With this PR, the Element class can be used as an interface class.
   This will allow us to create modified stubs for lxml where the _Element class
   is not mentioned at all.

   

   udifuchs committed Feb 17, 2024
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