Source code for pisak.properties

"""
Module for managing cooperation of different kinds of properties.
As most of the objects used by Pisak applications are GObjects and properties
of objects declared in JSON files are key factor in achieving their desired
behaviour, it is neccessary to translate between type of property understood
by GObject system and by python language.
"""


class PropertyAdapter:
    """
    Utility class for GObject vs python types of properties conversion.
    Contains gobject obligatory property setter and getter.
    When property of an object is declared in a JSON file, GObject property
    setter is called first and this, in turn, looks for related pythonic
    attribute with the same name and calls its setter.
    """

    def find_attribute(self, name):
        """
        Finds property of a given name.

        :param name: name of an attribute.

        :return: attribute.
        """
        name = self._repair_prop_name(name)
        for relative in self.__class__.mro():
            attribute = relative.__dict__.get(name)
            if attribute:
                break
        return attribute

    @staticmethod
    def _repair_prop_name(name):
        if '-' in name:
            name = name.replace('-', '_')
        return name

    def do_set_property(self, spec, value):
        """
        Introspect object properties and set the value.

        :param spec: specification of an attribute.
        :param value: new value that an attribute should be set with.
        """
        attribute = self.find_attribute(spec.name)
        if attribute is not None and isinstance(attribute, property):
            attribute.fset(self, value)
        else:
            raise ValueError("No such property", spec.name)

    def do_get_property(self, spec):
        """
        Introspect object properties and get the value.

        :param spec: specification of an attribute.

        :return: value of the found property.
        """
        attribute = self.find_attribute(spec.name)
        if attribute is not None and isinstance(attribute, property):
            return attribute.fget(self)
        else:
            raise ValueError("No such property", spec.name)