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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
def sort_priority(values, group):
# "x" new defined in local function helper
# "group" in outer function defined
def helper(x):#assign rank to every number to be sorted on
if x in group:
return (0, x)
return (1, x)
# values defined in function, sorting according to tuples
# see docstring
values.sort(key=helper)#key is function to rank in group ->0 else 1
# print(values.sort(key=helper))
"""# _summary_docstring
#see how the helper function classifies the lsit of numbers
[helper(x) for x in numbers]
[(0, 2), (0, 3), (0, 5), (0, 7), (1, 1), (1, 4), (1, 6), (1, 8)]
"""
# Example 2
#
# use sort_priority function to arrange numbers in list
# sort on tuples in group or not 0 or 1
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
group = {2, 3, 5, 7}
sort_priority(numbers, group)#rank number if in group first then other
print(numbers)
# Example 3
# found flag has to return if numbers in group are found
# scope of "found" is local to most inner function
# inner fuction is local for outer function so those variables apply
numbers=[]
print(numbers)
def sort_priority2(numbers, group):
found = False#use found to see scope level
def helper(x):
if x in group:
found = True # Seems simple found -> False outer function scope
#found -> True in inner function scope
return (0, x)
return (1, x)
numbers.sort(key=helper)#numbers list is changed by sort method with key
# always False helper function doesn't appy to outer function
return found#doesn't do much settle scope
# Example 4
# test on found with found flag in outer function
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
found = sort_priority2(numbers, group)#call for
print("Found:", found)
print(numbers)
# Example 5
# variable not defined when try to assign to other variable
try:
foo = does_not_exist * 5#var is not assigned before multiplication
except:
logging.exception("Expected")
else:
assert False
# Example 6
# scope is in different functions the inner cannot change outer scope
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
# Example 7
def sort_priority3(numbers, group):
found = False
# nonlocal will bring inner scop to nearest outer scope
# so here the nonlocal inner scope "found" can change the outer scope "found"
def helper(x):
nonlocal found # Added to make found var global overwrite outer found var
if x in group:
found = True
return (0, x)
return (1, x)
numbers.sort(key=helper)
return found#else found ->False with nonlocal found -> True
# Example 8
# test inner/outer scope with nonlocal variables
# found is now flag for numbers in group as "True"
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
found = sort_priority3(numbers, group)
assert found
print(found)
assert numbers == [2, 3, 5, 7, 1, 4, 6, 8]
# Example 9
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
group = {2, 3, 5, 7}
class Sorter:
def __init__(self, group):#init names of var
self.group = group #assign var
self.found = False #assign static bool
def __call__(self, x):
if x in self.group:
self.found = True
return (0, x)
return (1, x)
# initialize Sorter class with helper function(__call__)
# seems to get "found" in same scope as init function in the class
# nonlocal function can get out of the closure of the function(scope)
sorter = Sorter(group)#init class
numbers.sort(key=sorter)#use method from class as key
assert sorter.found is True#found is set in init and changed in call method same scope
assert numbers == [2, 3, 5, 7, 1, 4, 6, 8]