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item_027.py
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#!/usr/bin/env PYTHONHASHSEED=1234 python3
# Copyright 2014-2024 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.
### Start book environment setup
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)
### End book environment setup
print("Example 1")
visits = {
"Mexico": {"Tulum", "Puerto Vallarta"},
"Japan": {"Hakone"},
}
print("Example 2")
# Short
visits.setdefault("France", set()).add("Arles")
# Long
if (japan := visits.get("Japan")) is None:
visits["Japan"] = japan = set()
japan.add("Kyoto")
original_print = print
print = pprint
print(visits)
print = original_print
print("Example 3")
class Visits:
def __init__(self):
self.data = {}
def add(self, country, city):
city_set = self.data.setdefault(country, set())
city_set.add(city)
print("Example 4")
visits = Visits()
visits.add("Russia", "Yekaterinburg")
visits.add("Tanzania", "Zanzibar")
print(visits.data)
print("Example 5")
from collections import defaultdict
class Visits:
def __init__(self):
self.data = defaultdict(set)
def add(self, country, city):
self.data[country].add(city)
visits = Visits()
visits.add("England", "Bath")
visits.add("England", "London")
print(visits.data)