customizing.md

Customizing

Constant is just a plain old Python class, so if you want to add anything to it, just subclass it.

Custom Base Class

For example, you may want to create a subclass for your whole project that adds general features:

class CustomConstant( Constant ):
    def cname_in_mirror( self ):
        return self.cname[::-1]     # reverse string

Color = CustomConstant.define( "Color", "RED", "GREEN", "BLUE" )
Color.RED.cname_in_mirror()         # -> "DER"

Custom One-Off Class

If you want to create a custom class for only one value set — such as to add convenience properties specific to planets — start by creating a subclass:

class Planet( Constant ):
    @property
    def circumference( self ):
        return self.diameter * 3.14

Now, if you call Planet.define_set, it will construct and return a subclass of Planet, which is probably not what you want. If you want to populate the Planet class itself with a set of instances, skip define_set and instead call populate directly — which is the same method that define_set uses.

Planet.populate(
    Earth=dict( diameter=12742 ),
    Mars=dict(  diameter=6794  ),
)

Planet.Earth.circumference      # -> 40009.88

Example: Strict

This package includes a class which subclasses simpleset.Constant and overrides the populate method in order to enforce strictness when defining sets.

from simpleset.strict import Constant, StrictnessError

It will raise an exception if you mix forms:

try:
    Color = Constant.define_set( "Color", "RED", "GREEN", BLUE="0000ff" )
except StrictnessError:
    ...

Or if you don't specify the same set of attributes for all instances:

try:
    Foo = Constant.define_set( "Foo", A=dict( x=1 ), B=dict( y=2 ) )
except StrictnessError:
    ...

If you want to combine this feature with other mixins, import and use the mixin instead:

from simpleset import Constant
from simpleset.strict import StrictMixin
class MyConstant( StrictMixin, Constant ):
    pass