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extenum 0.8.0

Extended Enum classes for the Python 3 enum module

Extended Enum classes for the Python 3 enum module.

The enum module was added since 3.4. That’s good enough for simple use. The extenum is strongly inspired by Java Enum style described in Effective Java and provides additional feature.

How to install

NOTE: extenum supports Python 3 only.

$ pip install extenum

ConstantSpecificEnum

ConstantSpecificEnum class is inherited the standard Enum class and provides the feature of constant specific method and function overloading for Enum members.

Read Effective Java for more detail.

Constant specific method implementation

Let’s try to create Enum class with ConstantSpecificEnum. To use a method as function overloading, add @overload(CONSTANT) decorator on that method. The overload decorator is implicitly defined as well as you’ll see later in ImplicitEnum section.

>>> from extenum import ConstantSpecificEnum
>>> class Operation(ConstantSpecificEnum):
...     PLUS = '+'
...     MINUS = '-'
...     TIMES = '*'
...     DIVIDE = '/'
...
...     @overload(PLUS)
...     def apply(self, x, y):
...         return x + y
...
...     @overload(MINUS)
...     def apply(self, x, y):
...         return x - y
...
...     @overload(TIMES)
...     def apply(self, x, y):
...         return x * y
...
...     @overload(DIVIDE)
...     def apply(self, x, y):
...         return x / y
...
>>> for name, const in Operation.__members__.items():
...     print(name, ':', const.apply(2, 4))
...
PLUS : 6
MINUS : -2
TIMES : 8
DIVIDE : 0.5

Strategy enum pattern

The strategy enum is more complex pattern based on constant specific method.

>>> from extenum import ConstantSpecificEnum
>>> class PayrollDay(ConstantSpecificEnum):
...
...     class PayType(ConstantSpecificEnum):
...         WEEKDAY = 1
...         WEEKEND = 2
...
...         @overload(WEEKDAY)
...         def overtime_pay(self, hours, pay_rate):
...             return 0 if hours <= 8 else (hours - 8) * pay_rate / 2
...
...         @overload(WEEKEND)
...         def overtime_pay(self, hours, pay_rate):
...             return hours * pay_rate / 2
...
...         def pay(self, hours_worked, pay_rate):
...             base_pay = hours_worked * pay_rate
...             overtime_pay = self.overtime_pay(hours_worked, pay_rate)
...             return base_pay + overtime_pay
...
...     MONDAY = PayType.WEEKDAY
...     TUESDAY = PayType.WEEKDAY
...     WEDNESDAY = PayType.WEEKDAY
...     THURSDAY = PayType.WEEKDAY
...     FRIDAY = PayType.WEEKDAY
...     SATURDAY = PayType.WEEKEND
...     SUNDAY = PayType.WEEKEND
...
...     def pay(self, hours_worked, pay_rate):
...         return self.value.pay(hours_worked, pay_rate)
...
>>> PayrollDay.MONDAY.pay(10, 1000.0)
11000.0
>>> PayrollDay.WEDNESDAY.pay(8, 1000.0)
8000.0
>>> PayrollDay.SATURDAY.pay(10, 1000.0)
15000.0
>>> PayrollDay.SUNDAY.pay(8, 1000.0)
12000.0

ImplicitEnum

Before describing what ImplicitEnum class is, read good article written by Nick Coghlan as below.

OK. I guess you’ve already understood why the standard enum module haven’t supported implicit declaration syntax.

Put aside its needs for now, Nick indicates how to implement ImplicitEnum. So, let’s try to implement it experimentally using the special method, __missing__ in defaultdict and __prepare__ in Metaclass.

>>> from extenum import ImplicitEnum
>>> class Color(ImplicitEnum):
...     RED
...     GREEN
...     BLUE
...
>>> for name, const in Color.__members__.items():
...     print(name, ':', const.value)
...
RED : 1
GREEN : 2
BLUE : 3

It works well if some constants are explicit and the rest are implicit.

>>> class Numbers(ImplicitEnum):
...     ONE = 1
...     TWO = 2
...     THREE
...
>>> Numbers.THREE.value
3

However, it depends on the declaration order.

>>> class DuplicatedValues(ImplicitEnum):
...     ONE
...     TWO = 1
...     THREE = 1
...
>>> DuplicatedValues.ONE.value
1
>>> DuplicatedValues.TWO.value
1
>>> DuplicatedValues.THREE.value
1

EnumSet

EnumSet is one of the specialized implementation of Set interface for enumeration type, inspired by Java EnumSet.

It provides utility functions to handle multiple Enum constants.

>>> from enum import Enum
>>> from extenum import EnumSet
>>> class Mode(Enum):
...     READ = 4
...     WRITE = 2
...     EXECUTE = 1
...
...     @classmethod
...     def set_of(cls, values):
...         opts = EnumSet.none_of(cls)
...         for value in values:
...             opts.add(cls(value))
...         return opts
...
>>> Mode.set_of([4, 2])  # doctest: +SKIP
EnumSet({<Mode.READ: 4>, <Mode.WRITE: 2>})

To create EnumSet with all Enum members:

>>> EnumSet.all_of(Mode)  # doctest: +SKIP
EnumSet({<Mode.READ: 4>, <Mode.WRITE: 2>, <Mode.EXECUTE: 1>})

Or, to create EnumSet with arbitrary Enum members:

>>> enumset = EnumSet.of(Mode.READ, Mode.EXECUTE)
>>> enumset  # doctest: +SKIP
EnumSet({<Mode.READ: 4>, <Mode.EXECUTE: 1>})
>>> enumset.update(EnumSet.of(Mode.READ, Mode.WRITE))
>>> enumset  # doctest: +SKIP
EnumSet({<Mode.READ: 4>, <Mode.WRITE: 2>, <Mode.EXECUTE: 1>})

ChangeLog

0.8.0 (2015-03-15)

  • added EnumSet

0.7.0 (2015-03-06)

  • removed RegisterFactory for simplicity

0.6.0 (2015-03-05)

  • added ImplicitEnum

0.5.0 (2015-03-01)

  • first release
 
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