CLN/DOC: Remove sphinx referencing the wiki (#47853)

Author: mroeschke

doc/source/conf.py

@@ -453,7 +453,6 @@
 # extlinks alias
 extlinks = {
     "issue": ("https://github.com/pandas-dev/pandas/issues/%s", "GH"),
-    "wiki": ("https://github.com/pandas-dev/pandas/wiki/%s", "wiki "),
 }
 
 

web/pandas/about/roadmap.md

@@ -103,9 +103,52 @@ uses label-based, rather than position-based, indexing. We propose that
 it should only work with positional indexing, and the translation of
 keys to positions should be entirely done at a higher level.
 
-Indexing is a complicated API with many subtleties. This refactor will
-require care and attention. More details are discussed at
-<https://github.com/pandas-dev/pandas/wiki/(Tentative)-rules-for-restructuring-indexing-code>
+Indexing is a complicated API with many subtleties. This refactor will require care
+and attention. The following principles should inspire refactoring of indexing code and
+should result on cleaner, simpler, and more performant code.
+
+1. Label indexing must never involve looking in an axis twice for the same label(s).
+This implies that any validation step must either:
+
+  * limit validation to general features (e.g. dtype/structure of the key/index), or
+  * reuse the result for the actual indexing.
+
+2. Indexers must never rely on an explicit call to other indexers.
+For instance, it is OK to have some internal method of `.loc` call some
+internal method of `__getitem__` (or of their common base class),
+but never in the code flow of `.loc` should `the_obj[something]` appear.
+
+3. Execution of positional indexing must never involve labels (as currently, sadly, happens).
+That is, the code flow of a getter call (or a setter call in which the right hand side is non-indexed)
+to `.iloc` should never involve the axes of the object in any way.
+
+4. Indexing must never involve accessing/modifying values (i.e., act on `._data` or `.values`) more than once.
+The following steps must hence be clearly decoupled:
+
+  * find positions we need to access/modify on each axis
+  * (if we are accessing) derive the type of object we need to return (dimensionality)
+  * actually access/modify the values
+  * (if we are accessing) construct the return object
+
+5. As a corollary to the decoupling between 4.i and 4.iii, any code which deals on how data is stored
+(including any combination of handling multiple dtypes, and sparse storage, categoricals, third-party types)
+must be independent from code that deals with identifying affected rows/columns,
+and take place only once step 4.i is completed.
+
+  * In particular, such code should most probably not live in `pandas/core/indexing.py`
+  * ... and must not depend in any way on the type(s) of axes (e.g. no `MultiIndex` special cases)
+
+6. As a corollary to point 1.i, `Index` (sub)classes must provide separate methods for any desired validity check of label(s) which does not involve actual lookup,
+on the one side, and for any required conversion/adaptation/lookup of label(s), on the other.
+
+7. Use of trial and error should be limited, and anyway restricted to catch only exceptions
+which are actually expected (typically `KeyError`).
+
+  * In particular, code should never (intentionally) raise new exceptions in the `except` portion of a `try... exception`
+
+8. Any code portion which is not specific to setters and getters must be shared,
+and when small differences in behavior are expected (e.g. getting with `.loc` raises for
+missing labels, setting still doesn't), they can be managed with a specific parameter.
 
 ## Numba-accelerated operations