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# Copyright (c) 2012 - 2021, Anaconda, Inc., and Bokeh Contributors.
# All rights reserved.
#
# The full license is in the file LICENSE.txt, distributed with this software.
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""" Provide the ``Override`` class, for overriding base class property
attributes.
.. note::
This class should normally be imported from ``bokeh.core.properties``
instead of directly from this module.
"""
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# Boilerplate
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from __future__ import annotations
import logging # isort:skip
log = logging.getLogger(__name__)
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# Imports
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# Standard library imports
from typing import Generic, TypeVar
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# Globals and constants
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__all__ = (
'Override',
)
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# General API
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T = TypeVar("T")
[docs]class Override(Generic[T]):
""" Override attributes of Bokeh property in derived Models.
When subclassing a Bokeh Model, it may be desirable to change some of the
attributes of the property itself, from those on the base class. This is
accomplished using the ``Override`` class.
Currently, ``Override`` can only be use to override the ``default`` value
for the property.
Keyword Args:
default (obj) : a default value for this property on a subclass
Example:
Consider the following class definitions:
.. code-block:: python
from bokeh.model import Model
from bokeh.properties import Int, Override
class Parent(Model):
foo = Int(default=10)
class Child(Parent):
foo = Override(default=20)
The parent class has an integer property ``foo`` with default value
10. The child class uses the following code:
.. code-block:: python
foo = Override(default=20)
to specify that the default value for the ``foo`` property should be
20 on instances of the child class:
.. code-block:: python
>>> p = Parent()
>>> p.foo
10
>>> c = Child()
>>> c.foo
20
"""
default_overridden: bool
default: T
def __init__(self, *, default: T) -> None:
self.default_overridden = True
self.default = default
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# Dev API
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# Private API
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# Code
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