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# -*- coding: utf-8 -*-
"""
accessor.py contains base classes for implementing accessor properties
that can be mixed into or pinned onto other pandas classes.
"""
import warnings
from pandas.util._decorators import Appender
class DirNamesMixin(object):
_accessors = frozenset([])
_deprecations = frozenset(
['asobject', 'base', 'data', 'flags', 'itemsize', 'strides'])
def _dir_deletions(self):
""" delete unwanted __dir__ for this object """
return self._accessors | self._deprecations
def _dir_additions(self):
""" add additional __dir__ for this object """
rv = set()
for accessor in self._accessors:
try:
getattr(self, accessor)
rv.add(accessor)
except AttributeError:
pass
return rv
def __dir__(self):
"""
Provide method name lookup and completion
Only provide 'public' methods
"""
rv = set(dir(type(self)))
rv = (rv - self._dir_deletions()) | self._dir_additions()
return sorted(rv)
class PandasDelegate(object):
""" an abstract base class for delegating methods/properties """
def _delegate_property_get(self, name, *args, **kwargs):
raise TypeError("You cannot access the "
"property {name}".format(name=name))
def _delegate_property_set(self, name, value, *args, **kwargs):
raise TypeError("The property {name} cannot be set".format(name=name))
def _delegate_method(self, name, *args, **kwargs):
raise TypeError("You cannot call method {name}".format(name=name))
@classmethod
def _add_delegate_accessors(cls, delegate, accessors, typ,
overwrite=False):
"""
add accessors to cls from the delegate class
Parameters
----------
cls : the class to add the methods/properties to
delegate : the class to get methods/properties & doc-strings
acccessors : string list of accessors to add
typ : 'property' or 'method'
overwrite : boolean, default False
overwrite the method/property in the target class if it exists
"""
def _create_delegator_property(name):
def _getter(self):
return self._delegate_property_get(name)
def _setter(self, new_values):
return self._delegate_property_set(name, new_values)
_getter.__name__ = name
_setter.__name__ = name
return property(fget=_getter, fset=_setter,
doc=getattr(delegate, name).__doc__)
def _create_delegator_method(name):
def f(self, *args, **kwargs):
return self._delegate_method(name, *args, **kwargs)
f.__name__ = name
f.__doc__ = getattr(delegate, name).__doc__
return f
for name in accessors:
if typ == 'property':
f = _create_delegator_property(name)
else:
f = _create_delegator_method(name)
# don't overwrite existing methods/properties
if overwrite or not hasattr(cls, name):
setattr(cls, name, f)
def delegate_names(delegate, accessors, typ, overwrite=False):
"""
Add delegated names to a class using a class decorator. This provides
an alternative usage to directly calling `_add_delegate_accessors`
below a class definition.
Parameters
----------
delegate : the class to get methods/properties & doc-strings
acccessors : string list of accessors to add
typ : 'property' or 'method'
overwrite : boolean, default False
overwrite the method/property in the target class if it exists
Returns
-------
decorator
Examples
--------
@delegate_names(Categorical, ["categories", "ordered"], "property")
class CategoricalAccessor(PandasDelegate):
[...]
"""
def add_delegate_accessors(cls):
cls._add_delegate_accessors(delegate, accessors, typ,
overwrite=overwrite)
return cls
return add_delegate_accessors
# Ported with modifications from xarray
# https://github.com/pydata/xarray/blob/master/xarray/core/extensions.py
# 1. We don't need to catch and re-raise AttributeErrors as RuntimeErrors
# 2. We use a UserWarning instead of a custom Warning
class CachedAccessor(object):
"""Custom property-like object (descriptor) for caching accessors.
Parameters
----------
name : str
The namespace this will be accessed under, e.g. ``df.foo``
accessor : cls
The class with the extension methods. The class' __init__ method
should expect one of a ``Series``, ``DataFrame`` or ``Index`` as
the single argument ``data``
"""
def __init__(self, name, accessor):
self._name = name
self._accessor = accessor
def __get__(self, obj, cls):
if obj is None:
# we're accessing the attribute of the class, i.e., Dataset.geo
return self._accessor
accessor_obj = self._accessor(obj)
# Replace the property with the accessor object. Inspired by:
# http://www.pydanny.com/cached-property.html
# We need to use object.__setattr__ because we overwrite __setattr__ on
# NDFrame
object.__setattr__(obj, self._name, accessor_obj)
return accessor_obj
def _register_accessor(name, cls):
def decorator(accessor):
if hasattr(cls, name):
warnings.warn(
'registration of accessor {!r} under name {!r} for type '
'{!r} is overriding a preexisting attribute with the same '
'name.'.format(accessor, name, cls),
UserWarning,
stacklevel=2)
setattr(cls, name, CachedAccessor(name, accessor))
cls._accessors.add(name)
return accessor
return decorator
_doc = """Register a custom accessor on %(klass)s objects.
Parameters
----------
name : str
Name under which the accessor should be registered. A warning is issued
if this name conflicts with a preexisting attribute.
Notes
-----
When accessed, your accessor will be initialized with the pandas object
the user is interacting with. So the signature must be
.. code-block:: python
def __init__(self, pandas_object):
For consistency with pandas methods, you should raise an ``AttributeError``
if the data passed to your accessor has an incorrect dtype.
>>> pd.Series(['a', 'b']).dt
Traceback (most recent call last):
...
AttributeError: Can only use .dt accessor with datetimelike values
Examples
--------
In your library code::
import pandas as pd
@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 DataFrame
lat = self._obj.latitude
lon = 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:
>>> 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
See also
--------
%(others)s
"""
@Appender(_doc % dict(klass="DataFrame",
others=("register_series_accessor, "
"register_index_accessor")))
def register_dataframe_accessor(name):
from pandas import DataFrame
return _register_accessor(name, DataFrame)
@Appender(_doc % dict(klass="Series",
others=("register_dataframe_accessor, "
"register_index_accessor")))
def register_series_accessor(name):
from pandas import Series
return _register_accessor(name, Series)
@Appender(_doc % dict(klass="Index",
others=("register_dataframe_accessor, "
"register_series_accessor")))
def register_index_accessor(name):
from pandas import Index
return _register_accessor(name, Index)