ENH: Added public accessor registrar

LICENSES/XARRAY_LICENSE

@@ -0,0 +1,191 @@
+Apache License
+Version 2.0, January 2004
+http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+"License" shall mean the terms and conditions for use, reproduction, and
+distribution as defined by Sections 1 through 9 of this document.
+
+"Licensor" shall mean the copyright owner or entity authorized by the copyright
+owner that is granting the License.
+
+"Legal Entity" shall mean the union of the acting entity and all other entities
+that control, are controlled by, or are under common control with that entity.
+For the purposes of this definition, "control" means (i) the power, direct or
+indirect, to cause the direction or management of such entity, whether by
+contract or otherwise, or (ii) ownership of fifty percent (50%) or more of the
+outstanding shares, or (iii) beneficial ownership of such entity.
+
+"You" (or "Your") shall mean an individual or Legal Entity exercising
+permissions granted by this License.
+
+"Source" form shall mean the preferred form for making modifications, including
+but not limited to software source code, documentation source, and configuration
+files.
+
+"Object" form shall mean any form resulting from mechanical transformation or
+translation of a Source form, including but not limited to compiled object code,
+generated documentation, and conversions to other media types.
+
+"Work" shall mean the work of authorship, whether in Source or Object form, made
+available under the License, as indicated by a copyright notice that is included
+in or attached to the work (an example is provided in the Appendix below).
+
+"Derivative Works" shall mean any work, whether in Source or Object form, that
+is based on (or derived from) the Work and for which the editorial revisions,
+annotations, elaborations, or other modifications represent, as a whole, an
+original work of authorship. For the purposes of this License, Derivative Works
+shall not include works that remain separable from, or merely link (or bind by
+name) to the interfaces of, the Work and Derivative Works thereof.
+
+"Contribution" shall mean any work of authorship, including the original version
+of the Work and any modifications or additions to that Work or Derivative Works
+thereof, that is intentionally submitted to Licensor for inclusion in the Work
+by the copyright owner or by an individual or Legal Entity authorized to submit
+on behalf of the copyright owner. For the purposes of this definition,
+"submitted" means any form of electronic, verbal, or written communication sent
+to the Licensor or its representatives, including but not limited to
+communication on electronic mailing lists, source code control systems, and
+issue tracking systems that are managed by, or on behalf of, the Licensor for
+the purpose of discussing and improving the Work, but excluding communication
+that is conspicuously marked or otherwise designated in writing by the copyright
+owner as "Not a Contribution."
+
+"Contributor" shall mean Licensor and any individual or Legal Entity on behalf
+of whom a Contribution has been received by Licensor and subsequently
+incorporated within the Work.
+
+2. Grant of Copyright License.
+
+Subject to the terms and conditions of this License, each Contributor hereby
+grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free,
+irrevocable copyright license to reproduce, prepare Derivative Works of,
+publicly display, publicly perform, sublicense, and distribute the Work and such
+Derivative Works in Source or Object form.
+
+3. Grant of Patent License.
+
+Subject to the terms and conditions of this License, each Contributor hereby
+grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free,
+irrevocable (except as stated in this section) patent license to make, have
+made, use, offer to sell, sell, import, and otherwise transfer the Work, where
+such license applies only to those patent claims licensable by such Contributor
+that are necessarily infringed by their Contribution(s) alone or by combination
+of their Contribution(s) with the Work to which such Contribution(s) was
+submitted. If You institute patent litigation against any entity (including a
+cross-claim or counterclaim in a lawsuit) alleging that the Work or a
+Contribution incorporated within the Work constitutes direct or contributory
+patent infringement, then any patent licenses granted to You under this License
+for that Work shall terminate as of the date such litigation is filed.
+
+4. Redistribution.
+
+You may reproduce and distribute copies of the Work or Derivative Works thereof
+in any medium, with or without modifications, and in Source or Object form,
+provided that You meet the following conditions:
+
+You must give any other recipients of the Work or Derivative Works a copy of
+this License; and
+You must cause any modified files to carry prominent notices stating that You
+changed the files; and
+You must retain, in the Source form of any Derivative Works that You distribute,
+all copyright, patent, trademark, and attribution notices from the Source form
+of the Work, excluding those notices that do not pertain to any part of the
+Derivative Works; and
+If the Work includes a "NOTICE" text file as part of its distribution, then any
+Derivative Works that You distribute must include a readable copy of the
+attribution notices contained within such NOTICE file, excluding those notices
+that do not pertain to any part of the Derivative Works, in at least one of the
+following places: within a NOTICE text file distributed as part of the
+Derivative Works; within the Source form or documentation, if provided along
+with the Derivative Works; or, within a display generated by the Derivative
+Works, if and wherever such third-party notices normally appear. The contents of
+the NOTICE file are for informational purposes only and do not modify the
+License. You may add Your own attribution notices within Derivative Works that
+You distribute, alongside or as an addendum to the NOTICE text from the Work,
+provided that such additional attribution notices cannot be construed as
+modifying the License.
+You may add Your own copyright statement to Your modifications and may provide
+additional or different license terms and conditions for use, reproduction, or
+distribution of Your modifications, or for any such Derivative Works as a whole,
+provided Your use, reproduction, and distribution of the Work otherwise complies
+with the conditions stated in this License.
+
+5. Submission of Contributions.
+
+Unless You explicitly state otherwise, any Contribution intentionally submitted
+for inclusion in the Work by You to the Licensor shall be under the terms and
+conditions of this License, without any additional terms or conditions.
+Notwithstanding the above, nothing herein shall supersede or modify the terms of
+any separate license agreement you may have executed with Licensor regarding
+such Contributions.
+
+6. Trademarks.
+
+This License does not grant permission to use the trade names, trademarks,
+service marks, or product names of the Licensor, except as required for
+reasonable and customary use in describing the origin of the Work and
+reproducing the content of the NOTICE file.
+
+7. Disclaimer of Warranty.
+
+Unless required by applicable law or agreed to in writing, Licensor provides the
+Work (and each Contributor provides its Contributions) on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied,
+including, without limitation, any warranties or conditions of TITLE,
+NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. You are
+solely responsible for determining the appropriateness of using or
+redistributing the Work and assume any risks associated with Your exercise of
+permissions under this License.
+
+8. Limitation of Liability.
+
+In no event and under no legal theory, whether in tort (including negligence),
+contract, or otherwise, unless required by applicable law (such as deliberate
+and grossly negligent acts) or agreed to in writing, shall any Contributor be
+liable to You for damages, including any direct, indirect, special, incidental,
+or consequential damages of any character arising as a result of this License or
+out of the use or inability to use the Work (including but not limited to
+damages for loss of goodwill, work stoppage, computer failure or malfunction, or
+any and all other commercial damages or losses), even if such Contributor has
+been advised of the possibility of such damages.
+
+9. Accepting Warranty or Additional Liability.
+
+While redistributing the Work or Derivative Works thereof, You may choose to
+offer, and charge a fee for, acceptance of support, warranty, indemnity, or
+other liability obligations and/or rights consistent with this License. However,
+in accepting such obligations, You may act only on Your own behalf and on Your
+sole responsibility, not on behalf of any other Contributor, and only if You
+agree to indemnify, defend, and hold each Contributor harmless for any liability
+incurred by, or claims asserted against, such Contributor by reason of your
+accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS
+
+APPENDIX: How to apply the Apache License to your work
+
+To apply the Apache License to your work, attach the following boilerplate
+notice, with the fields enclosed by brackets "[]" replaced with your own
+identifying information. (Don't include the brackets!) The text should be
+enclosed in the appropriate comment syntax for the file format. We also
+recommend that a file or class name and description of purpose be included on
+the same "printed page" as the copyright notice for easier identification within
+third-party archives.
+
+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.

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 +140,44 @@ As an example of fully-formed metadata:
          'metadata': None}
     ],
     'pandas_version': '0.20.0'}
+
+.. _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.

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

@@ -119,6 +119,56 @@ Current Behavior
 
     s.rank(na_option='top')
 
+
+Extending Pandas Objects with New Accessors
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Pandas uses accessors to group together many related methods into a namespace on
+``Series`` or ``Index`` objects. For example, ``Series.str`` for string methods,
+or ``Series.dt`` for datetime methods. Inspired by xarray, pandas now officially
+supports registering custom accessors in library code.
+
+Once you've implemented an accessor, register it with one or more of the decorators
+
+* :func:`pandas.api.extensions.register_dataframe_accessor`
+* :func:`pandas.api.extensions.register_series_accessor`
+* :func:`pandas.api.extensions.register_index_accessor`
+
+.. code-block:: python
+
+   import pandas as pd
+
+   @pd.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
+
+Back in an interactive IPython session:
+
+.. code-block:: python
+
+   >>> 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 provides a convenient alternative to subclassing or composition.
+If you write a custom accessor, make a pull request adding it to our
+:ref:`ecosystem` page.
+
 .. _whatsnew_0230.enhancements.other:
 
 Other Enhancements

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)