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"""Utilities for meta-estimators"""
# Author: Joel Nothman
# Andreas Mueller
# License: BSD
from operator import attrgetter
from functools import update_wrapper
import numpy as np
from ..utils import safe_indexing
__all__ = ['if_delegate_has_method']
class _IffHasAttrDescriptor(object):
"""Implements a conditional property using the descriptor protocol.
Using this class to create a decorator will raise an ``AttributeError``
if none of the delegates (specified in ``delegate_names``) is an attribute
of the base object or the first found delegate does not have an attribute
``attribute_name``.
This allows ducktyping of the decorated method based on
``delegate.attribute_name``. Here ``delegate`` is the first item in
``delegate_names`` for which ``hasattr(object, delegate) is True``.
See https://docs.python.org/3/howto/descriptor.html for an explanation of
descriptors.
"""
def __init__(self, fn, delegate_names, attribute_name):
self.fn = fn
self.delegate_names = delegate_names
self.attribute_name = attribute_name
# update the docstring of the descriptor
update_wrapper(self, fn)
def __get__(self, obj, type=None):
# raise an AttributeError if the attribute is not present on the object
if obj is not None:
# delegate only on instances, not the classes.
# this is to allow access to the docstrings.
for delegate_name in self.delegate_names:
try:
delegate = attrgetter(delegate_name)(obj)
except AttributeError:
continue
else:
getattr(delegate, self.attribute_name)
break
else:
attrgetter(self.delegate_names[-1])(obj)
# lambda, but not partial, allows help() to work with update_wrapper
out = lambda *args, **kwargs: self.fn(obj, *args, **kwargs)
# update the docstring of the returned function
update_wrapper(out, self.fn)
return out
def if_delegate_has_method(delegate):
"""Create a decorator for methods that are delegated to a sub-estimator
This enables ducktyping by hasattr returning True according to the
sub-estimator.
Parameters
----------
delegate : string, list of strings or tuple of strings
Name of the sub-estimator that can be accessed as an attribute of the
base object. If a list or a tuple of names are provided, the first
sub-estimator that is an attribute of the base object will be used.
"""
if isinstance(delegate, list):
delegate = tuple(delegate)
if not isinstance(delegate, tuple):
delegate = (delegate,)
return lambda fn: _IffHasAttrDescriptor(fn, delegate,
attribute_name=fn.__name__)
def _safe_split(estimator, X, y, indices, train_indices=None):
"""Create subset of dataset and properly handle kernels."""
from ..gaussian_process.kernels import Kernel as GPKernel
if (hasattr(estimator, 'kernel') and callable(estimator.kernel) and
not isinstance(estimator.kernel, GPKernel)):
# cannot compute the kernel values with custom function
raise ValueError("Cannot use a custom kernel function. "
"Precompute the kernel matrix instead.")
if not hasattr(X, "shape"):
if getattr(estimator, "_pairwise", False):
raise ValueError("Precomputed kernels or affinity matrices have "
"to be passed as arrays or sparse matrices.")
X_subset = [X[index] for index in indices]
else:
if getattr(estimator, "_pairwise", False):
# X is a precomputed square kernel matrix
if X.shape[0] != X.shape[1]:
raise ValueError("X should be a square kernel matrix")
if train_indices is None:
X_subset = X[np.ix_(indices, indices)]
else:
X_subset = X[np.ix_(indices, train_indices)]
else:
X_subset = safe_indexing(X, indices)
if y is not None:
y_subset = safe_indexing(y, indices)
else:
y_subset = None
return X_subset, y_subset
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