Source code for pyface.data_view.data_models.data_accessors
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# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
# the conditions described in the aforementioned license. The license
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""" Classes for extracting data from objects
This module provides helper classes for the row table data model and
related classes for extracting data from an object in a consistent way.
"""
from abc import abstractmethod
from collections.abc import Hashable, MutableMapping, MutableSequence
from traits.api import (
ABCHasStrictTraits, Any, Event, Instance, Int, Str, observe
)
from traits.trait_base import xgetattr, xsetattr
from pyface.data_view.abstract_data_model import DataViewSetError
from pyface.data_view.abstract_value_type import AbstractValueType
from pyface.data_view.value_types.api import TextValue
[docs]class AbstractDataAccessor(ABCHasStrictTraits):
""" Accessor that gets and sets data on an object.
"""
#: A human-readable label for the accessor.
title = Str()
#: The value type of the title of this accessor, suitable for use in a
#: header.
title_type = Instance(AbstractValueType, factory=TextValue)
#: The value type of the data accessed.
value_type = Instance(AbstractValueType)
#: An event fired when accessor is updated update. The payload is
#: a tuple of the accessor info and whether the title or value changed
#: (or both).
updated = Event
[docs] @abstractmethod
def get_value(self, obj):
""" Return a value for the provided object.
Parameters
----------
obj : Any
The object that contains the data.
Returns
-------
value : Any
The data value contained in the object.
"""
raise NotImplementedError()
[docs] def can_set_value(self, obj):
""" Return whether the value can be set on the provided object.
Parameters
----------
obj : Any
The object that contains the data.
Returns
-------
can_set_value : bool
Whether or not the value can be set.
"""
return False
[docs] def set_value(self, obj, value):
""" Set the value on the provided object.
Parameters
----------
obj : Any
The object that contains the data.
value : Any
The data value to set.
Raises
-------
DataViewSetError
If setting the value fails.
"""
raise DataViewSetError(
"Cannot set {!r} column of {!r}.".format(self.title, obj)
)
# trait observers
@observe('title,title_type.updated')
def _title_updated(self, event):
self.updated = (self, 'title')
@observe('value_type.updated')
def _value_type_updated(self, event):
self.updated = (self, 'value')
[docs]class ConstantDataAccessor(AbstractDataAccessor):
""" DataAccessor that returns a constant value.
"""
#: The value to return.
value = Any()
[docs] def get_value(self, obj):
""" Return the value ignoring the provided object.
Parameters
----------
obj : Any
An object.
Returns
-------
value : Any
The data value contained in this class' value trait.
"""
return self.value
@observe('value')
def _value_updated(self, event):
self.updated = (self, 'value')
[docs]class AttributeDataAccessor(AbstractDataAccessor):
""" DataAccessor that presents an extended attribute on an object.
This is suitable for use with Python objects, including HasTraits
classes.
"""
#: The extended attribute name of the trait holding the value.
attr = Str()
[docs] def get_value(self, obj):
""" Return the attribute value for the provided object.
Parameters
----------
obj : Any
The object that contains the data.
Returns
-------
value : Any
The data value contained in the object's attribute.
"""
return xgetattr(obj, self.attr)
[docs] def can_set_value(self, obj):
""" Return whether the value can be set on the provided object.
Parameters
----------
obj : Any
The object that contains the data.
Returns
-------
can_set_value : bool
Whether or not the value can be set.
"""
return bool(self.attr)
[docs] def set_value(self, obj, value):
if not self.can_set_value(obj):
raise DataViewSetError(
"Attribute is not specified for {!r}".format(self)
)
xsetattr(obj, self.attr, value)
@observe('attr')
def _attr_updated(self, event):
self.updated = (self, 'value')
def _title_default(self):
# create human-friendly version of extended attribute
attr = self.attr.split('.')[-1]
title = attr.replace('_', ' ').title()
return title
[docs]class IndexDataAccessor(AbstractDataAccessor):
""" DataAccessor that presents an index on a sequence object.
This is suitable for use with a sequence.
"""
#: The index in a sequence which holds the value.
index = Int()
[docs] def get_value(self, obj):
""" Return the indexed value for the provided object.
Parameters
----------
obj : sequence
The object that contains the data.
Returns
-------
value : Any
The data value contained in the object at the index.
"""
return obj[self.index]
[docs] def can_set_value(self, obj):
""" Return whether the value can be set on the provided object.
Parameters
----------
obj : Any
The object that contains the data.
Returns
-------
can_set_value : bool
Whether or not the value can be set.
"""
return isinstance(obj, MutableSequence) and 0 <= self.index < len(obj)
[docs] def set_value(self, obj, value):
""" Set the value on the provided object.
Parameters
----------
obj : Any
The object that contains the data.
value : Any
The data value to set.
Raises
-------
DataViewSetError
If setting the value fails.
"""
if not self.can_set_value(obj):
raise DataViewSetError(
"Cannot set {!r} index of {!r}.".format(self.index, obj)
)
obj[self.index] = value
@observe('index')
def _index_updated(self, event):
self.updated = (self, 'value')
def _title_default(self):
title = str(self.index)
return title
[docs]class KeyDataAccessor(AbstractDataAccessor):
""" DataAccessor that presents an item on a mapping object.
This is suitable for use with a mapping, such as a dictionary.
"""
#: The key in the mapping holding the value.
key = Instance(Hashable)
[docs] def get_value(self, obj):
""" Return the key's value for the provided object.
Parameters
----------
obj : mapping
The object that contains the data.
Returns
-------
value : Any
The data value contained in the given key of the object.
"""
return obj[self.key]
[docs] def can_set_value(self, obj):
""" Set the value on the provided object.
Parameters
----------
obj : mapping
The object that contains the data.
value : Any
The data value to set.
Raises
-------
DataViewSetError
If setting the value fails.
"""
return isinstance(obj, MutableMapping)
[docs] def set_value(self, obj, value):
""" Set the value on the provided object.
Parameters
----------
obj : Any
The object that contains the data.
value : Any
The data value to set.
Raises
-------
DataViewSetError
If setting the value fails.
"""
if not self.can_set_value(obj):
raise DataViewSetError(
"Cannot set {!r} key of {!r}.".format(self.key, obj)
)
obj[self.key] = value
@observe('key')
def _key_updated(self, event):
self.updated = (self, 'value')
def _title_default(self):
title = str(self.key).title()
return title
