#!/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

stock = {

"nails": 125,

"screws": 35,

"wingnuts": 8,

"washers": 24,

}

order = ["screws", "wingnuts", "clips"]

# floor division 1,5 =>1

def get_batches(count, size):

return count // size

result = {}#init result as dict

for name in order:

# get defaults to 0 if no values are specified

count = stock.get(name, 0)

#print(count)

# get defaults to 8 if no values are specified

batches = get_batches(count, 8)#size ->8

print(batches)

# if batches is True, then add to result dict key/value => name: batches

if batches:#batches >0 ->true then add new key/value to dict

result[name] = batches

print(result)

# Example 2

# found is a set with comprehension cerate a dict name: batches

# use function get_batches if name not in stock get defaults to 0

# if name in list order then use function get_batches again to get existing batches

# order = ["screws", "wingnuts", "clips"]

found = {#dict comprehension create stucture name/size pair as expression filled by for loop over order by name present in stock

name: get_batches(stock.get(name, 0), 8)#expression part

for name in order

if get_batches(stock.get(name, 0), 8)

}

print(found)

# Example 3

# create has_bag set see "found" set but now for batches of 4 instead of 8

has_bug = {

name: get_batches(stock.get(name, 0), 4)#all element with size 4

for name in order

if get_batches(stock.get(name, 0), 8)#select just the ones with size 8 so found within has_bags

}

print("Expected:", found)

print("Found: ", has_bug)

# Example 4

# use ":=" for assigning value/batches if name is in order

# get default 0 if the name is not in stock returns false else True if in stock

# then found is set {name: batches}

found = {#dict with str/int pair as expression and for loop over list to get elements

name: batches #expression

for name in order

if (batches := get_batches(stock.get(name, 0), 8))#assign return of finc to var with ":="

}

assert found == {"screws": 4, "wingnuts": 1}

print(found)

# Example 5

try:

# test for names in stock where count//10 > 0

# create new variable "tenth" assign if name/size pair in stock > 10 then True

# add to result {name: size/10 >0}

# bring assign to if block if referencing "tenth" variable later in comprehension

result = {

name: (tenth := count // 10) #cut of divide by 10 assign to var as expression for dict comprehension

for name, count in stock.items()

if tenth > 0 #use calculated value ftom str/int pair to filter

}

except:

logging.exception("Expected")

else:

assert False # True then return is empty set

print(result)

print(tenth)

# Example 6

# sort of initialize "tenth" later assign in if block

result = {

name: tenth #str/int pair in dict as expression in dict comprehension

for name, count in stock.items() #for loop over dict

if (tenth := count // 10) > 0}#calculated and assign and filter in one go

print(result)

# Example 7

# create list determine division 2 assign to "last" variable

# loops over values in stock

half = [

(last := count // 2) #assign calculated value to var in expression for list comprehension

for count in stock.values()#for loop over values of name/value pairs in dict

]

print(f"Last item of {half} is {last}")

# Example 8

# leak means variable in expression leaks in the loop else better to have

# error=> variable unknown to loop

for count in stock.values(): # Leaks loop variable loop till last then print

pass

print(f"Last item of {list(stock.values())} is {count}")

# Example 9

# here "count" is not in the same scope as half no leaking of count variable

try:

del count#del var

half = [

count // 2 #expression with count as index in comprehension only ->del in outer scope

for count in stock.values()

]

print(half) # Works

print(count) # Exception because loop variable didn't leak

#NameError: name 'count' is not defined

except:

logging.exception("Expected")

else:

assert False

# Example 10

# see assign values to "batches" in if block return tuple with next statement

# as iterator over "found" tuple

found = (

(name, batches) #expression str/int tuple in tuple comprehension

for name in order #for loop over list

if (batches := get_batches(stock.get(name, 0), 8))#assign value to var for str/int tuple

)

print(next(found))#next needed for next item by generator

print(next(found))#other next needed for other next item by generator