effectivepython/example_code/item_41.py at master · sharc007/effectivepython · GitHub

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#!/usr/bin/env PYTHONHASHSEED=1234 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.

# Reproduce book environment

import random

random.seed(1234)

import logging

from pprint import pprint

from sys import stdout as STDOUT

# Write all output to a temporary directory

import atexit

import gc

import io

import os

import tempfile

TEST_DIR = tempfile.TemporaryDirectory()

atexit.register(TEST_DIR.cleanup)

# Make sure Windows processes exit cleanly

OLD_CWD = os.getcwd()

atexit.register(lambda: os.chdir(OLD_CWD))

os.chdir(TEST_DIR.name)

def close_open_files():

everything = gc.get_objects()

for obj in everything:

if isinstance(obj, io.IOBase):

obj.close()

atexit.register(close_open_files)

# Example 1

class ToDictMixin:

def to_dict(self):

return self._traverse_dict(self.__dict__)

# Example 2

def _traverse_dict(self, instance_dict):

output = {}

for key, value in instance_dict.items():

output[key] = self._traverse(key, value)

return output

def _traverse(self, key, value):

if isinstance(value, ToDictMixin):

return value.to_dict()

elif isinstance(value, dict):

return self._traverse_dict(value)

elif isinstance(value, list):

return [self._traverse(key, i) for i in value]

elif hasattr(value, '__dict__'):

return self._traverse_dict(value.__dict__)

else:

return value

# Example 3

class BinaryTree(ToDictMixin):

def __init__(self, value, left=None, right=None):

self.value = value

self.left = left

self.right = right

# Example 4

tree = BinaryTree(10,

left=BinaryTree(7, right=BinaryTree(9)),

right=BinaryTree(13, left=BinaryTree(11)))

orig_print = print

print = pprint

print(tree.to_dict())

print = orig_print

# Example 5

class BinaryTreeWithParent(BinaryTree):

def __init__(self, value, left=None,

right=None, parent=None):

super().__init__(value, left=left, right=right)

self.parent = parent

# Example 6

def _traverse(self, key, value):

if (isinstance(value, BinaryTreeWithParent) and

key == 'parent'):

return value.value # Prevent cycles

else:

return super()._traverse(key, value)

# Example 7

root = BinaryTreeWithParent(10)

root.left = BinaryTreeWithParent(7, parent=root)

root.left.right = BinaryTreeWithParent(9, parent=root.left)

orig_print = print

print = pprint

print(root.to_dict())

print = orig_print

# Example 8

class NamedSubTree(ToDictMixin):

def __init__(self, name, tree_with_parent):

self.name = name

self.tree_with_parent = tree_with_parent

my_tree = NamedSubTree('foobar', root.left.right)

orig_print = print

print = pprint

print(my_tree.to_dict()) # No infinite loop

print = orig_print

# Example 9

import json

class JsonMixin:

@classmethod

def from_json(cls, data):

kwargs = json.loads(data)

return cls(**kwargs)

def to_json(self):

return json.dumps(self.to_dict())

# Example 10

class DatacenterRack(ToDictMixin, JsonMixin):

def __init__(self, switch=None, machines=None):

self.switch = Switch(**switch)

self.machines = [

Machine(**kwargs) for kwargs in machines]

class Switch(ToDictMixin, JsonMixin):

def __init__(self, ports=None, speed=None):

self.ports = ports

self.speed = speed

class Machine(ToDictMixin, JsonMixin):

def __init__(self, cores=None, ram=None, disk=None):

self.cores = cores

self.ram = ram

self.disk = disk

# Example 11

serialized = """{

"switch": {"ports": 5, "speed": 1e9},

"machines": [

{"cores": 8, "ram": 32e9, "disk": 5e12},

{"cores": 4, "ram": 16e9, "disk": 1e12},

{"cores": 2, "ram": 4e9, "disk": 500e9}

]

}"""

deserialized = DatacenterRack.from_json(serialized)

roundtrip = deserialized.to_json()

assert json.loads(serialized) == json.loads(roundtrip)

effectivepython/example_code/item_41.py at master · sharc007/effectivepython · GitHub

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