ENH: Added public accessor registrar

LICENSES/XARRAY_LICENSE

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doc/source/api.rst

@@ -2498,6 +2498,20 @@ Scalar introspection
     api.types.is_re_compilable
     api.types.is_scalar
 
+Extensions
+----------
+
+These are primarily intented for library authors looking to extend pandas
+objects.
+
+.. currentmodule:: pandas
+
+.. autosummary::
+   :toctree: generated/
+
+   api.extensions.register_dataframe_accessor
+   api.extensions.register_series_accessor
+   api.extensions.register_index_accessor
 
 .. This is to prevent warnings in the doc build. We don't want to encourage
 .. these methods.

doc/source/developer.rst

@@ -140,3 +140,46 @@ As an example of fully-formed metadata:
          'metadata': None}
     ],
     'pandas_version': '0.20.0'}
+
+.. _developer.register-accessors:
+
+Registering Custom Accessors
+----------------------------
+
+Libraries can use the decorators
+:func:`pandas.api.extensions.register_dataframe_accessor`,
+:func:`pandas.api.extensions.register_series_accessor`, and
+:func:`pandas.api.extensions.register_index_accessor`, to add additional "namespaces" to
+pandas objects. All of these follow a similar convention: you decorate a class, providing the name of attribute to add. The
+class's `__init__` method gets the object being decorated. For example:
+
+.. ipython:: python
+
+   @pd.api.extensions.register_dataframe_accessor("geo")
+   class GeoAccessor(object):
+       def __init__(self, pandas_obj):
+           self._obj = pandas_obj
+
+       @property
+       def center(self):
+           # return the geographic center point of this DataFarme
+           lon = self._obj.latitude
+           lat = self._obj.longitude
+           return (float(lon.mean()), float(lat.mean()))
+
+       def plot(self):
+           # plot this array's data on a map, e.g., using Cartopy
+           pass
+
+Now users can access your methods using the `geo` namespace:
+
+      >>> ds = pd.DataFrame({'longitude': np.linspace(0, 10),
+      ...                    'latitude': np.linspace(0, 20)})
+      >>> ds.geo.center
+      (5.0, 10.0)
+      >>> ds.geo.plot()
+      # plots data on a map
+
+This can be a convenient way to extend pandas objects without subclassing them.
+If you write a custom accessor, make a pull request adding it to our
+:ref:`ecosystem` page.

doc/source/internals.rst

@@ -100,6 +100,8 @@ Subclassing pandas Data Structures
 
   2. Use *composition*. See `here <http://en.wikipedia.org/wiki/Composition_over_inheritance>`_.
 
+  3. Extending by :ref:`registering an accessor <internals.register-accessors>`
+
 This section describes how to subclass ``pandas`` data structures to meet more specific needs. There are 2 points which need attention:
 
 1. Override constructor properties.

doc/source/whatsnew/v0.23.0.txt

@@ -145,6 +145,13 @@ Other Enhancements
 - ``Resampler`` objects now have a functioning :attr:`~pandas.core.resample.Resampler.pipe` method.
   Previously, calls to ``pipe`` were diverted to  the ``mean`` method (:issue:`17905`).
 - :func:`~pandas.api.types.is_scalar` now returns ``True`` for ``DateOffset`` objects (:issue:`18943`).
+- Added :func:`pandas.api.extensions.register_dataframe_accessor`,
+  :func:`pandas.api.extensions.register_series_accessor`, and
+  :func:`pandas.api.extensions.register_index_accessor`, accessor for libraries downstream of pandas
+  to register custom accessors like ``.cat`` on pandas objects. See
+  :ref:`Registering Custom Accessors <developer.register-accessors>` for more (:issue:`14781`).
+
+
 
 .. _whatsnew_0230.api_breaking:
 

pandas/api/__init__.py

@@ -1 +1,2 @@
 """ public toolkit API """
+from . import types, extensions  # noqa

pandas/api/extensions/__init__.py

@@ -0,0 +1,4 @@
+"""Public API for extending panadas objects."""
+from pandas.core.accessor import (register_dataframe_accessor,  # noqa
+                                  register_index_accessor,
+                                  register_series_accessor)