DOC: clean up internals.rst (#51107)

* DOC: clean up internals.rst

* add some links

Author: topper-123

doc/source/development/internals.rst

@@ -15,24 +15,24 @@ Indexing
 In pandas there are a few objects implemented which can serve as valid
 containers for the axis labels:
 
-* ``Index``: the generic "ordered set" object, an ndarray of object dtype
+* :class:`Index`: the generic "ordered set" object, an ndarray of object dtype
   assuming nothing about its contents. The labels must be hashable (and
   likely immutable) and unique. Populates a dict of label to location in
   Cython to do ``O(1)`` lookups.
 * ``Int64Index``: a version of ``Index`` highly optimized for 64-bit integer
   data, such as time stamps
 * ``Float64Index``: a version of ``Index`` highly optimized for 64-bit float data
-* ``MultiIndex``: the standard hierarchical index object
-* ``DatetimeIndex``: An Index object with ``Timestamp`` boxed elements (impl are the int64 values)
-* ``TimedeltaIndex``: An Index object with ``Timedelta`` boxed elements (impl are the in64 values)
-* ``PeriodIndex``: An Index object with Period elements
+* :class:`MultiIndex`: the standard hierarchical index object
+* :class:`DatetimeIndex`: An Index object with :class:`Timestamp` boxed elements (impl are the int64 values)
+* :class:`TimedeltaIndex`: An Index object with :class:`Timedelta` boxed elements (impl are the in64 values)
+* :class:`PeriodIndex`: An Index object with Period elements
 
 There are functions that make the creation of a regular index easy:
 
-* ``date_range``: fixed frequency date range generated from a time rule or
+* :func:`date_range`: fixed frequency date range generated from a time rule or
   DateOffset. An ndarray of Python datetime objects
-* ``period_range``: fixed frequency date range generated from a time rule or
-  DateOffset. An ndarray of ``Period`` objects, representing timespans
+* :func:`period_range`: fixed frequency date range generated from a time rule or
+  DateOffset. An ndarray of :class:`Period` objects, representing timespans
 
 The motivation for having an ``Index`` class in the first place was to enable
 different implementations of indexing. This means that it's possible for you,
@@ -43,28 +43,28 @@ From an internal implementation point of view, the relevant methods that an
 ``Index`` must define are one or more of the following (depending on how
 incompatible the new object internals are with the ``Index`` functions):
 
-* ``get_loc``: returns an "indexer" (an integer, or in some cases a
+* :meth:`~Index.get_loc`: returns an "indexer" (an integer, or in some cases a
   slice object) for a label
-* ``slice_locs``: returns the "range" to slice between two labels
-* ``get_indexer``: Computes the indexing vector for reindexing / data
+* :meth:`~Index.slice_locs`: returns the "range" to slice between two labels
+* :meth:`~Index.get_indexer`: Computes the indexing vector for reindexing / data
   alignment purposes. See the source / docstrings for more on this
-* ``get_indexer_non_unique``: Computes the indexing vector for reindexing / data
+* :meth:`~Index.get_indexer_non_unique`: Computes the indexing vector for reindexing / data
   alignment purposes when the index is non-unique. See the source / docstrings
   for more on this
-* ``reindex``: Does any pre-conversion of the input index then calls
+* :meth:`~Index.reindex`: Does any pre-conversion of the input index then calls
   ``get_indexer``
-* ``union``, ``intersection``: computes the union or intersection of two
+* :meth:`~Index.union`, :meth:`~Index.intersection`: computes the union or intersection of two
   Index objects
-* ``insert``: Inserts a new label into an Index, yielding a new object
-* ``delete``: Delete a label, yielding a new object
-* ``drop``: Deletes a set of labels
-* ``take``: Analogous to ndarray.take
+* :meth:`~Index.insert`: Inserts a new label into an Index, yielding a new object
+* :meth:`~Index.delete`: Delete a label, yielding a new object
+* :meth:`~Index.drop`: Deletes a set of labels
+* :meth:`~Index.take`: Analogous to ndarray.take
 
 MultiIndex
 ~~~~~~~~~~
 
-Internally, the ``MultiIndex`` consists of a few things: the **levels**, the
-integer **codes** (until version 0.24 named *labels*), and the level **names**:
+Internally, the :class:`MultiIndex` consists of a few things: the **levels**, the
+integer **codes**, and the level **names**:
 
 .. ipython:: python
 
@@ -80,13 +80,13 @@ You can probably guess that the codes determine which unique element is
 identified with that location at each layer of the index. It's important to
 note that sortedness is determined **solely** from the integer codes and does
 not check (or care) whether the levels themselves are sorted. Fortunately, the
-constructors ``from_tuples`` and ``from_arrays`` ensure that this is true, but
-if you compute the levels and codes yourself, please be careful.
+constructors :meth:`~MultiIndex.from_tuples` and :meth:`~MultiIndex.from_arrays` ensure
+that this is true, but if you compute the levels and codes yourself, please be careful.
 
 Values
 ~~~~~~
 
-pandas extends NumPy's type system with custom types, like ``Categorical`` or
+pandas extends NumPy's type system with custom types, like :class:`Categorical` or
 datetimes with a timezone, so we have multiple notions of "values". For 1-D
 containers (``Index`` classes and ``Series``) we have the following convention: