Source code for pyface.data_view.data_models.data_accessors

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# license included in LICENSE.txt and may be redistributed only under
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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