Anaconda Enterprise: Documentation

# bokeh.core.property.descriptor_factory

Provide a Base class for all Bokeh properties.

Bokeh properties work by contributing Python descriptor objects to `HasProps` classes. These descriptors then delegate attribute access back to the Bokeh property class, which handles validation, serialization, and documentation needs.

The `PropertyDescriptorFactory` class provides two methods `autocreate` and `make_descriptors` that are used by the metaclass `MetaHasProps` during class creation to create and install the necessary descriptors corresponding to the declared properties.

This machinery helps to make Bokeh much more user friendly. For example, the DataSpec properties mediate between fixed values and references to column data source columns. A user can use a very simple syntax, and the property will correctly serialize and validate automatically:

    from bokeh.models import Circle

    c = Circle()

    c.x = 10      # serializes to {'value': 10}

    c.x = 'foo'   # serializes to {'field': 'foo'}

    c.x = [1,2,3] # raises a ValueError validation exception

There are many other examples like this throughout Bokeh. In this way users may operate simply and naturally, and not be concerned with the low-level details around validation, serialization, and documentation.

Note

These classes form part of the very low-level machinery that implements the Bokeh model and property system. It is unlikely that any of these classes or their methods will be applicable to any standard usage or to anyone who is not directly developing on Bokeh’s own infrastructure.

class `bokeh.core.property.descriptor_factory.``PropertyDescriptorFactory`

  Base class for all Bokeh properties.

  A Bokeh property really consist of two parts: the familar “property” portion, such as `Int`, `String`, etc., as well as an associated Python descriptor that delegates attribute access (e.g. `range.start`) to the property instance.

  Consider the following class definition:

      from bokeh.model import Model
      from bokeh.core.properties import Int

      class SomeModel(Model):
          foo = Int(default=10)

  Then we can observe the following:

      >>> m = SomeModel()

      # The class itself has had a descriptor for 'foo' installed
      >>> getattr(SomeModel, 'foo')
      <bokeh.core.property.descriptors.BasicPropertyDescriptor at 0x1065ffb38>

      # which is used when 'foo' is accessed on instances
      >>> m.foo
      10

  classmethod `autocreate`()

    Called by the `MetaHasProps` metaclass to create a new instance of this descriptor when the property is assigned using only the property type. For example:

        class Foo(Model):

            bar = String   # no parens used here

  `make_descriptors`(name)

    Return a list of `PropertyDescriptor` instances to install on a class, in order to delegate attribute access to this property.

    Parameters: | name (str) – the name of the property these descriptors are for
    Returns: | list[PropertyDescriptor]

    The descriptors returned are collected by the `MetaHasProps` metaclass and added to `HasProps` subclasses during class creation.

    Subclasses of `PropertyDescriptorFactory` are responsible for implementing this function to return descriptors specific to their needs.