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item_38.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
names = ['Socrates', 'Archimedes', 'Plato', 'Aristotle']
names.sort(key=len)#sort will mutate list
print(names)
# Example 2
def log_missing():
print('Key added')
return 0
print(log_missing())#invoke func with print and return
# Example 3
from collections import defaultdict
current = {'green': 12, 'blue': 3}#create key/int dict
increments = [#create list of tuples
('red', 5),
('blue', 17),
('orange', 9),
]
result = defaultdict(log_missing, current)#use of log func unclear
print('Before:', dict(result))
for key, amount in increments:#loop over list of tuples add to dict key/int pairs and update int
result[key] += amount
print('After: ', dict(result))
# Example 4
def increment_with_report(current, increments):#func on dict at list of tuples
added_count = 0#init var
def missing():
nonlocal added_count # Stateful closure as global var -> outside func
added_count += 1
return 0
result = defaultdict(missing, current)#calls missing func for item not in dict
for key, amount in increments:
result[key] += amount
return result, added_count
# Example 5
result, count = increment_with_report(current, increments)
assert count == 2#called for missing item in dict
print(count)
print(result)
# Example 6
class CountMissing:
def __init__(self):
self.added = 0
def missing(self):
self.added += 1
return 0
# Example 7
counter = CountMissing()#initiate new class to create counter
result = defaultdict(counter.missing, current) # Method ref use start value for new items in dict
for key, amount in increments:
result[key] += amount
assert counter.added == 2
print(counter.added)
print(result)
# Example 8
class BetterCountMissing:
def __init__(self):
self.added = 0
def __call__(self):
self.added += 1
return 0
counter = BetterCountMissing()
assert counter() == 0
assert callable(counter)
# Example 9
counter = BetterCountMissing()#initiate new class counter
result = defaultdict(counter, current) # Relies on __call__ use start value add count new items in default dict
for key, amount in increments:
result[key] += amount
assert counter.added == 2
print(result)