python refactoring blog

animal-class.py

class Animal:
  def __init__(self, *, has_scales=False, lays_eggs=False, drinks_milk=False):
    self.has_scales = has_scales
    self.lays_eggs = lays_eggs
    self.drinks_milk = drinks_milk

animal-pet-finish.py

class Animal:
  def __init__(self, age, *, has_scales=False, lays_eggs=False, drinks_milk=False):
    self.age = age
    self.has_scales = has_scales
    self.lays_eggs = lays_eggs
    self.drinks_milk = drinks_milk

        
class Pet:
  def __init__(self, name, animal):
    self.name = name
    self.animal = animal
    self.treats_eaten = 0

  def give_treats(self, count):
    self.treats_eaten += count

  @property
  def needs_heat_lamp(self):
    return (
      self.animal.has_scales and
      self.animal.lays_eggs and
      not self.animal.drinks_milk)

  @property
  def age(self):
    raise AttributeError('Must use animal.age')

  @age.setter
  def age(self, new_age):
    raise AttributeError('Must assign animal.age')

attrerror.py

@property
def age(self):
  raise AttributeError('Must use animal.age')

bool-class.py

class OystersGood:
  def __init__(self, month):
    lowered = month.lower()
    self.r = lowered.endswith('r')
    self.ary = lowered.endswith('ary')
    self._result = self.r or self.ary

  def __bool__(self):  # aka __nonzero__
    return self._result
...
time_for_oysters = OystersGood(month)
if time_for_oysters:  # Calls __bool__
  print('%s: oysters' % month)

# test
test = OystersGood('November')
assert test
assert test.r
assert not test.ary

boolexpr-fuction.py

def oysters_good(month):
  lowered = month.lower()
  return (
      lowered.endswith('r') or
      lowered.endswith('ary'))
...
# extract boolean expression as function
if oysters_good(month):
  print('%s: oysters' % month)

# extract boolean expression as variable from function
time_for_oysters = oysters_good(month)
if time_for_oysters:
  print('%s: oysters' % month)

boolexpr-variable.py

lowered = month.lower()
ends_in_r = lowered.endswith('r')
ends_in_ary = lowered.endswith('ary')

if ends_in_r or ends_in_ary:
  print('%s: oysters' % month)

check-kwargs.py

class Pet:
  def __init__(self, name, age_or_animal, maybe_animal=None):
    self.name = name

  if maybe_animal is not None:
    warnings.warn('Should specify "age" for Animal')
    self.animal = maybe_animal
    self.animal.age = age_or_animal
  else:
    self.animal = age_or_animal

expression.py

if (month.lower().endswith('r') or 
      month.lower().endswith('ary')):
    print('%s: oysters' % month)

field.py

class Pet:
  @property
  def has_scales(self):
    warnings.warn('Use animal.has_scales instead')
    return self.animal.has_scales

helper.py

class Pet:
  def give_treats(self, count):
    self.treats_eaten += count

pet-class.py

class Pet:
  def __init__(self, name, age, *,
               has_scales=False,
               lays_eggs=False,
               drinks_milk=False):
    self.name = name
    self.age = age
    self.treats_eaten = 0
    self.has_scales = has_scales
    self.lays_eggs = lays_eggs
    self.drinks_milk = drinks_milk

  @property
  def needs_heat_lamp(self):
    return (
      self.has_scales and
      self.lays_eggs and
      not self.drinks_milk)

pet-with-parameter.py

class Pet:
  def __init__(self, name, age, animal=None, **kwargs):
    self.name = name
    self.age = age
    self.treats_eaten = 0

    if kwargs and animal is not None:
      raise TypeError('Must supply either an Animal instance or keyword arguments')

    if animal is None:
      warnings.warn('Must directly pass an Animal instance')
      animal = Animal(**kwargs)

setter.py

@age.setter
def age(self, new_age):
  warnings.warn('Should assign animal.age')
  self.animal.age = new_age