What is free_properties?

free_properties is a python package that features the FreeProperty class. A FreePropety object behaves just like its value property, allowing it to be used as a proxy for get, and set calculations like a python property.

Installation

Get the latest version of free_properties from https://pypi.python.org/pypi/free_properties/

If you have an installation of Python with pip, simple install it with:

$ pip install free_properties

To get the git version, run:

$ git clone git://github.com/yoelcortes/free_properties

Documentation

free_properties’s documentation is available on the web:

http://free_properties.readthedocs.io/

Getting started

The PropertyFactory is a FreeProperty class creator that functions similar to Python ‘property’ objects. Use the PropertyFactory to create a Weight class which calculates weight based on density and volume:

>>> from free_properties import PropertyFactory
>>> def getter(self):
...    '''Weight (kg) based on volume (m^3).'''
...    data = self.data
...    rho = data['rho'] # Density (kg/m^3)
...    vol = data['vol'] # Volume (m^3)
...    return rho * vol
>>>
>>> def setter(self, weight):
...    data = self.data
...    rho = data['rho'] # Density (kg/m^3)
...    data['vol'] = weight / rho
>>>
>>> # Initialize with a value getter, setter, and the class name.
>>> Weight = PropertyFactory(getter, setter, 'Weight', units='kg')

It is more convinient to use the PropertyFactory as a decorator:

>>> @PropertyFactory(units='kg')
>>> def Weight(self):
...    '''Weight (kg) based on volume (m^3).'''
...    data = self.data
...    rho = data['rho'] # Density (kg/m^3)
...    vol = data['vol'] # Volume (m^3)
...    return rho * vol
>>>
>>> @Weight.setter
>>> def Weight(self, weight):
...    data = self.data
...    rho = data['rho'] # Density (kg/m^3)
...    data['vol'] = weight / rho

Create dictionaries of data and initialize new Weight objects:

>>> water_data = {'rho': 1000, 'vol': 3}
>>> ethanol_data = {'rho': 789, 'vol': 3}
>>> weight_water = Weight('Water', water_data)
>>> weight_ethanol = Weight('Ethanol', ethanol_data)
>>> weight_water
<Water: 3000 kg>
>>> weight_ethanol
<Ethanol: 2367 kg>

These properties behave just like their dynamic value:

>>> weight_water + 30
3030
>>> weight_water + weight_ethanol
5367

Get and set the value through the ‘value’ attribute:

>>> weight_water.value
3000
>>> weight_water.value = 4000
>>> weight_water.value
4000
>>> water_data # Note that the volume changed too
{'rho': 1000, 'vol': 4}

In place magic methods will also change the property value:

>>> weight_water -= 1000
>>> weight_water
<Weight(Water): 3000 kg>
>>> water_data  # The change also affects the original data
{'rho': 1000, 'vol': 3}

Use the property_array to manage free properties as an array:

>>> from free_properties import property_array
>>> prop_arr = property_array([weight_water, weight_ethanol])
>>> prop_arr
property_array([3000.0, 2367.0], dtype=object)
>>> prop_arr.sum()
5367.0

Changing the values of a property_array changes the value of its properties:

>>> # Addition in place
>>> prop_arr += 3000
>>> prop_arr
property_array([6000.0, 5367.0], dtype=object)
>>> # Note how the data also changes
>>> water_data
{'rho': 1000, 'vol': 6.0}
>>> ethanol_data
{'rho': 789, 'vol': 6.802281368821292}
>>> # Setting an item changes the property value
>>> prop_arr[1] = 2367
>>> ethanol_data
{'rho': 789, 'vol': 3}

New arrays have no connection to the property_array:

>>> prop_arr - 1000 #  Returns a new array
array([5000.0, 1367.0], dtype=object)
>>> water_data #  Data remains unchanged
{'rho': 1000, 'vol': 6.0}

Latest source code

The latest development version of free_properties’s sources can be obtained at:

https://github.com/yoelcortes/free_properties

Bug reports

To report bugs, please use the free_properties’ Bug Tracker at:

https://github.com/yoelcortes/free_properties

License information

See LICENSE.txt for information on the terms & conditions for usage of this software, and a DISCLAIMER OF ALL WARRANTIES.

Although not required by the free_properties’ license, if it is convenient for you, please cite free_properties if used in your work. Please also consider contributing any changes you make back, and benefit the community.

Citation

To cite free_properties in publications use:

Yoel Cortes-Pena (2019). free_properties: Manage properties outside a class.
https://github.com/yoelcortes/free_properties