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#!/usr/bin/env PYTHONHASHSEED=1234 python3
# Copyright 2014-2019 Brett Slatkin, Pearson Education Inc.
#
# 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)