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item_033.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")
def sort_priority(values, group):
def helper(x):
if x in group:
return (0, x)
return (1, x)
values.sort(key=helper)
print("Example 2")
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
group = {2, 3, 5, 7}
sort_priority(numbers, group)
print(numbers)
print("Example 3")
def sort_priority2(numbers, group):
found = False # Flag initial value
def helper(x):
if x in group:
found = True # Flip the flag
return (0, x)
return (1, x)
numbers.sort(key=helper)
return found # Flag final value
print("Example 4")
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
found = sort_priority2(numbers, group)
print("Found:", found)
print(numbers)
print("Example 5")
try:
foo = does_not_exist * 5
except:
logging.exception('Expected')
else:
assert False
print("Example 6")
def sort_priority2(numbers, group):
found = False # Scope: 'sort_priority2'
def helper(x):
if x in group:
found = True # Scope: 'helper' -- Bad!
return (0, x)
return (1, x)
numbers.sort(key=helper)
return found
print("Example 7")
def sort_priority3(numbers, group):
found = False
def helper(x):
nonlocal found # Added
if x in group:
found = True
return (0, x)
return (1, x)
numbers.sort(key=helper)
return found
print("Example 8")
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
found = sort_priority3(numbers, group)
print("Found:", found)
print(numbers)
print("Example 9")
class Sorter:
def __init__(self, group):
self.group = group
self.found = False
def __call__(self, x):
if x in self.group:
self.found = True
return (0, x)
return (1, x)
print("Example 10")
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
sorter = Sorter(group)
numbers.sort(key=sorter)
print("Found:", sorter.found)
print(numbers)