Python addendum to Metz's Practical Object-Oriented Design in Ruby

ch3.py

# For original code, see "some_framework.py"

# Remove Argument-Order Dependencies

# First code example under "Use Hashes for Initialization Arguments"
class Gear(object):
    def __init__(self, **kwargs):
        self.chainring = kwargs['chainring']
        self.cog = kwargs['cog']
        self.wheel = kwargs['wheel']
    # ...

print(Gear(chainring=52, cog=11, wheel=Wheel(26, 1.5)).gear_inches)

# "Explicitly Define Defaults"
class Gear(object):
    def __init__(self, chainring=40, cog=18, **kwargs):
        self.chainring = chainring
        self.cog = cog
        self.wheel = kwargs['wheel']
    # ...

driver.py

from some_framework import Wheel
import gear_wrapper

print(gear_wrapper.gear(chainring=52, cog=11, wheel=Wheel(26, 1.5)).gear_inches)

gear_wrapper.py

import some_framework

def gear(**kwargs):
    return some_framework.Gear(kwargs['chainring'], kwargs['cog'], kwargs['wheel'])

some_framework.py

from collections import namedtuple

class Wheel(namedtuple('Wheel', 'rim tire')):
    @property
    def diameter(self):
        return self.rim + (self.tire * 2)

class Gear(object):
    def __init__(self, chainring, cog, wheel):
        self.chainring = chainring
        self.cog = cog
        self.wheel = wheel

    @property
    def ratio(self):
        return self.chainring / self.cog

    @property
    def gear_inches(self):
        return self.ratio * self.wheel.diameter