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item_17.py
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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
visits = {
"Mexico": {"Tulum", "Puerto Vallarta"},
"Japan": {"Hakone"},
}
print(visits)
# Example 2
# assign key set to key if not {} add value to set
visits.setdefault("France", set())#assign set() as key/value -> 'key:set()'
print(visits)
visits.setdefault("France", set()).add("Arles") # Short replace set() in key/set() pair by add method
print(visits)
# assign value to set of the key else get method defaults to "None"
# test on "None" then assign empty set {}
if (japan := visits.get("Japan")) is None: # Long look for key in dict with key/set pairs
visits["Japan"] = japan = set() #set set() to key/set() pair in dict and assign set() to var japan
print(japan)#var japan
japan.add("Kyoto")#replace set() in var japan if empty else add to existing element in key/set
# swap print statement with pprint
original_print = print
print = pprint
print(visits)
pprint(visits)
# swap print statement with pprint reverse
print = original_print
# Example 3
# make class with city add method
class Visits:
def __init__(self):
self.data = {}#set data to empty set {}
def add(self, country, city):
# make key,set combinations within data set
city_set = self.data.setdefault(country, set())#assign key/set() or existing key/set to dict city_set
city_set.add(city)
# Example 4
# initialize visits variable from class Visits:
visits = Visits()#assign class object to visits
print(visits)
# use add method from class Visits to add cities to countries set
visits.add("Russia", "Yekaterinburg")#use add method from class Visits
visits.add("Tanzania", "Zanzibar")
print(visits.data)#use data method from class Visits
# Example 5
from collections import defaultdict
# default creates default value for every key so every as a value is to add to
class Visits:
def __init__(self):
self.data = defaultdict(set)
def add(self, country, city):
self.data[country].add(city)
visits = Visits()
print(visits.data)#defaultdict(<class 'set'>, {})
#visits.add("England",set())
print(visits.data)
visits.add("England", "Bath")#assign key/set pair to dict
visits.add("England", "London")#assign set to existing key/set pair ->add method from class Visits needs key/set pair as input
print(visits.data)