WIP/ DOC: Move 'For Developers' content from wiki to contributing docs. #30232

doc/source/development/contributing.rst

@@ -569,8 +569,40 @@ do not make sudden changes to the code that could have the potential to break
 a lot of user code as a result, that is, we need it to be as *backwards compatible*
 as possible to avoid mass breakages.
 
-Additional standards are outlined on the `code style wiki
-page <https://github.com/pandas-dev/pandas/wiki/Code-Style-and-Conventions>`_.
+Cross-compatible code
+---------------------
+
+It's important to write code that will be compatible with most recent version of
+Python 3.
+
+Python 2/3 Compatibility
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+* After `v0.25.0 <https://github.com/pandas-dev/pandas/releases/tag/v0.25.0>`_
+  we have stopped supporting Python 2.
+* ``callable`` - was first removed from Python 3.0 then brought  back in python
+  3.2.
+
+Imports (aim for absolute)
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In Python 3, everything is an absolute import, so doing something like: ``import
+string`` will import the string module rather than ``string.py`` in the same directory.
+As much as possible, you should try to write out absolute imports that show the
+whole import chain from toplevel pandas. In test code, it might be easier to just
+reference local variables with relative imports (that start with ``.``) for clarity,
+but in other code better to be explicit.
+
+::
+
+    # cross compatible and preferred
+    import pandas.core.common as com
+
+    # may FAIL in Python 3
+    import common
+
+    # okay in test code
+    from .common import test_base
 
 Optional dependencies
 ---------------------