{
    "info": {
        "author": "Andrew M. Hogan",
        "author_email": "drewthedruid@gmail.com",
        "bugtrack_url": null,
        "classifiers": [
            "Intended Audience :: Developers",
            "License :: OSI Approved :: Apache Software License",
            "Operating System :: OS Independent",
            "Programming Language :: Python",
            "Programming Language :: Python :: 3",
            "Topic :: Software Development :: Libraries :: Python Modules",
            "Topic :: Utilities"
        ],
        "description": "# Promised\n\n### promise\n\nA flexible delayed-evaluation cached property with get/set/del/init capabilities for inter-property relationships.\n\n### linked\n\nA dependency-managing promise which will refresh dependent properties when any of its linker methods are called. (typically, deleter and setter)\n\n### Member\n\nA cached-mapping extension class designed for the @promise decorator, similar to explicitly (im-)mutable memoization.\n\n## Get\n\nType this into terminal / command-line:\n```\npip install promised\n```\n\nAnd this into Python:\n```\nfrom promised import promise, linked, Member  # linked are dependent promises, Member is for cached-mapping extension.\n```\n\n## Purpose\nThis project currently functions as an easy method for managing property dependencies, for example:\n\n```\nclass _TestLine(object):\n    @linked\n    def length(self):\n        self._length = 2.0\n```\n```\nclass _TestSquare(object):\n    @linked(chain=True)\n    def side(self):\n        self._side = _TestLine()\n\n    @side.chain(\"length\")\n    def width(self):\n        self._width = self.side.length\n\n    @side.chain(\"length\")\n    def height(self):\n        self._height = self.side.length\n\n    @width.linked\n    @height.linked\n    def area(self):\n        self._area = self.width * self.height\n```\n```\nclass _TestBox(object):\n    \"\"\"This is a test class for linked promises. I don't know what more you're expecting.\"\"\"\n    @linked(chain=True)\n    def side(self):\n        self._side = _TestLine()\n\n    @linked(chain=True)\n    def base(self):\n        self._base = _TestSquare()\n\n    @side.chain(\"length\")\n    @base.chain(\"area\")\n    def volume(self):\n        self._volume = self.base.area * self.side.length\n```\n```\ndef _test_area():\n    box = _TestBox()\n    assert box.volume == 8.0, \"Box volume is 2.0 * 2.0 * 2.0 as Line's default length is 2.0\"\n    box.side.length = 4\n    assert box.volume == 16.0, \"Box volume has updated due to change in side's length.\"\n    box.base.side.length = 10\n    assert box.volume == 400.0, \"Box volume has update due to change in base's side length.\"\n    line = _TestLine()\n    line.length = 0.5\n    box.side = line\n    assert box.volume == 50.0, \"Box volume has updated due to changed side.\"\n```\n\nThis started because I found myself doing this too often:\n```\n@property\ndef property_public_name(self):\n    '''Why am I typing the same lines with tiny changes in every project all the time?'''\n    try:\n        return self._property_public_name_with_leading_underscore\n    except AttributeError:\n        self._property_public_name_with_leading_underscore = self._method_to_calculate_property()\n    return self._property_public_name_with_leading_underscore\n```\n\n## Usage\n\nNow, it looks like this:\n```\n@promise\ndef property_public_name(self):\n    '''Now this is promising!'''\n    self._property_public_name_with_leading_underscore = self._method_to_calculate_property()\n```\n\nIt's still accessed like this:\n```\nproperty_value = self.property_public_name\n```\n\nAnd you can still do this:\n```\n@property_public_name.setter\n@property_public_name.deleter\n@property_public_name.getter\n```\n\nYou can group a bunch of promises up with the same keeper by passing in the name of the private variable (the variable initially set in the promise's keeper) to the promise's \\_\\_init\\_\\_:\n```\ndef _set_associated_properties(self):\n    associated_map_one = {}\n    associated_map_two = {}\n    for thing in self.iterable:\n        associated_map_one = thing.map_one(associated_map_one)\n        associated_map_two = thing.map_two(associated_map_two)\n    self._property_one_public_name = associated_map_one\n    self._property_two_public_name = associated_map_two\n\nproperty_one_public_name = promised(_set_associated_properties, name=\"_property_one_public_name\")\nproperty_two_public_name = promised(_set_associated_properties, name=\"_property_two_public_name\")\n```\nYou can link dependent attributes together using an @linked property (which functions similarly to a promised property) and decorating any of the dependent properties' getter / setter / deleter / keeper methods with the @linked_property_name.linked decorator a single time per dependent property:\n```\n@linked\ndef heroes(self):\n    self._heroes = None\n\n@heroes.linked\n@promise\ndef future_of_townsville(self):\n    self._future_of_townsville = \"Bleak\" if not self.heroes else \"FAN-tastic!\"\n\n@future_of_townsville.deleter\ndef future_of_townsville(self):\n    del self._future_of_townsville\n\n@heroes.linker\n@heroes.setter\ndef heroes(self, value):\n    self._heroes = value\n\ndef test_town_turnaround(self):\n    \"\"Setting self.heroes to a different value should reset its dependent properties.\"\"\"\n    assert not hasattr(self, \"_heroes\"), \"promise should not have already been kept!\"\n    assert not hasattr(self, \"_future_of_townsville\"), \"promise should not have already been kept!\"\n    assert self.future_of_townsville == \"Bleak\", \"There should be no heroes - yet!\"\n    assert self.heroes is None, \"There should be no heroes - yet!\"\n    self.heroes = \"POWER-PUFF GIRLS\"\n    assert not hasattr(self, \"_future_of_townsville\"), \"The future of townsville is dependent on heroes, so it should be deleted once changed!\"\n    assert self.future_of_townsville == \"FAN-tastic!\", \"The future of townsville should be looking up!\"\n```\n\n@linked properties will automatically refresh dependent properties when a @linker method of theirs is called. For ease of use, as this will require at least a deletion method in dependent properties, @linked properties are @promise properties with default deleters and setters which are also default linkers. Using defaults on linked properties, the previous example becomes:\n```\n@linked\ndef heroes(self):\n    self._heroes = None\n\n@heroes.linked\ndef future_of_townsville(self):\n    self._future_of_townsville = \"Bleak\" if not self.heroes else \"FAN-tastic!\"\n\ndef test_town_turnaround(self):\n    \"\"Setting self.heroes to a different value should reset its dependent properties.\"\"\"\n    ...\n```\n\nSee documentation in boiler_property.py for further details on removing default deleters / setters / linkers:\n```\n@linked(linkers=(\"keeper\",)\ndef property_which_refreshes_dependent_properties_when_keeper_method_used(self):\n    \"\"\"This would typically reset all dependent properties after this property is accessed for the first time and first access post-refresh/deletion.\"\"\"\n    self._property_which_refreshes_dependent_properties_when_keeper_method_used = \"RESET\"\n\n@linked(deleter=False, setter=False, linkers=(\"getter\",)\ndef read_only_property_which_refreshes_dependent_properties_on_every_access(self):\n    \"\"\"Not advised for properties which access this property once reset (as the typical dependent property would.)\"\"\"\n    self._read_only_property_which_refreshes_dependent_properties_on_every_access = None\n```\n\nYou can use the chain=True init argument of @linked properties to designate an inter-class dependency source.\n```\n@linked(chain=True)\ndef side(self):\n    self._side = _TestLine()\n\n@linked(chain=True)\ndef base(self):\n    self._base = _TestSquare()\n```\n\nAnd use @dependency_source.chain(\"dependent_property_name\") to mimic the intra-class behavior of @property_name.linked.\n```\n@side.chain(\"length\")\n@base.chain(\"area\")\ndef volume(self):\n    self._volume = self.base.area * self.side.length\n```\n\nYou can use the Member class to create a cached promised property which varies on input (like memoization, but explicitly mutable / not-mutable):\n```\ndef _children_of_parent_with_attribute_value(self, parent, child_attribute_value):\n    return self.parent_children_map[parent] & self.attribute_value_to_set_of_objects_map[child_attribute_value]\n\n@promise\ndef adult_children(self):\n    self._adult_children = Member(self._children_of_parent_with_attribute_value, \"The White House\")\n```\n\nWhich is then accessed like this:\n```\ndonnie = countries.adult_children[\"America\"]\n```\n\n## Future\n\nThese are just the first steps in patterns I've recognized as useful for explicit cached properties, and I'm very interested in building in more automated support for associated & dependent properties - please feel free to share any suggestions.\n\n## Copyright\n\npromised module by Andrew M. Hogan. (promised © 2019 Hogan Consulting Group)\n\n## License\n\nLicensed under the Apache License.\n\n\n",
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