effectivepython/example_code/item_35.py at master · AISTLAB/effectivepython · GitHub

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#!/usr/bin/env python3

# Licensed under the Apache License, Version 2.0 (the "License");

# you may not use this file except in compliance with the License.

# You may obtain a copy of the License at

# http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software

# distributed under the License is distributed on an "AS IS" BASIS,

# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

# See the License for the specific language governing permissions and

# limitations under the License.

# Preamble to mimick book environment

import logging

from pprint import pprint

from sys import stdout as STDOUT

# Example 1

class Field(object):

def __init__(self, name):

self.name = name

self.internal_name = '_' + self.name

def __get__(self, instance, instance_type):

if instance is None: return self

return getattr(instance, self.internal_name, '')

def __set__(self, instance, value):

setattr(instance, self.internal_name, value)

# Example 2

class Customer(object):

# Class attributes

first_name = Field('first_name')

last_name = Field('last_name')

prefix = Field('prefix')

suffix = Field('suffix')

# Example 3

foo = Customer()

print('Before:', repr(foo.first_name), foo.__dict__)

foo.first_name = 'Euclid'

print('After: ', repr(foo.first_name), foo.__dict__)

# Example 4

class Meta(type):

def __new__(meta, name, bases, class_dict):

for key, value in class_dict.items():

if isinstance(value, Field):

value.name = key

value.internal_name = '_' + key

cls = type.__new__(meta, name, bases, class_dict)

return cls

# Example 5

class DatabaseRow(object, metaclass=Meta):

pass

# Example 6

class Field(object):

def __init__(self):

# These will be assigned by the metaclass.

self.name = None

self.internal_name = None

def __get__(self, instance, instance_type):

if instance is None: return self

return getattr(instance, self.internal_name, '')

def __set__(self, instance, value):

setattr(instance, self.internal_name, value)

# Example 7

class BetterCustomer(DatabaseRow):

first_name = Field()

last_name = Field()

prefix = Field()

suffix = Field()

# Example 8

foo = BetterCustomer()

print('Before:', repr(foo.first_name), foo.__dict__)

foo.first_name = 'Euler'

print('After: ', repr(foo.first_name), foo.__dict__)

effectivepython/example_code/item_35.py at master · AISTLAB/effectivepython · GitHub

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