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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
import itertools
# Example 2
# itertools creates iterator => one list out of multiple lists
it = itertools.chain([1, 2, 3], [4, 5, 6])#compare with list comprehension loop over listst
print(list(it))
# Example 3
# repeats 3 times "hello"string
it = itertools.repeat("hello", 3)#3*"string"
print(list(it))
# Example 4
# calls next 10 times on iterator use the list to cycle over till 10 items
it = itertools.cycle([1, 2])
result = [next(it) for _ in range(10)]#cycle method extends list with itself as needed
print(result)
# Example 5
# iterate for creating several list with "list" method on iterator int is 3 cycles/variables
it1, it2, it3 = itertools.tee(["first", "second"], 3)#method tee return list int = vars else error
print(list(it1))
print(list(it2))
print(list(it3))
# Example 6
keys = ["one", "two", "three"]
values = [1, 2]
# zip joins list key/value combinations up to shortest list length => 3 versus 2 gives 2 list of 2 values
normal = list(zip(keys, values))#takes shortest list as base for combinations as tuples in list
print("zip: ", normal)
# zip_longest joins list key/value combinations up to longest list length default for missing values
it = itertools.zip_longest(keys, values, fillvalue="nope")#use itertools to force base longest list for combinations withdefault for missing
longest = list(it)
print("zip_longest:", longest)
# Example 7
values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
# generates slice call with "list" method
first_five = itertools.islice(values, 5)#part of list
print("First five: ", list(first_five))
# generates slice call => start,stop,step on values =>with "list" method
middle_odds = itertools.islice(values, 2, 8, 2)#every second from slice 2-8 beginning from 0,1,2->
print("Middle odds:", list(middle_odds))
# Example 8
# filter through values with lambda function as argument in generator, call with "list" method
values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
less_than_seven = lambda x: x < 7#anon func values <7 so called predicate
it = itertools.takewhile(less_than_seven, values)#takes <7
print(list(it))
# Example 9
# drop/filter out items from list, return leftover with "list" method
values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
less_than_seven = lambda x: x < 7#anon func <7 [1, 2, 3, 4, 5, 6]
it = itertools.dropwhile(less_than_seven, values)#drops <7 [7, 8, 9, 10]
print(list(it))
# Example 10
# use filter method to mod 2 items from values
# list method as iterator over filter result
values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
evens = lambda x: x % 2 == 0#anon func dividable by 2
filter_result = filter(evens, values)#return iterator if func is true
print(filter_result)#returns filter object
print("Filter: ", list(filter_result))
# filterfalse method of itertools as complement of filter method
filter_false_result = itertools.filterfalse(evens, values)#returns complement of func where false
print("Filter false:", list(filter_false_result))
# Example 11
# method accumulate of itertools adds up progressive
values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
sum_reduce = itertools.accumulate(values)#create iterator over list with method accumalate progressive sum
print("Sum: ", list(sum_reduce))
# take n ste + n st + 1 value then the mod 20
def sum_modulo_20(first, second):#return result of modulo 20 rest piece
output = first + second
return output % 20
# function takes cum values n and (n+1) them mod 20
modulo_reduce = itertools.accumulate(values, sum_modulo_20)#for every progressive sum the rest of modulo 20
print("Modulo:", list(modulo_reduce))
# Example 12
# is product 2x2 combinations
# like this [(1, 1), (1, 2), (2, 1), (2, 2)]
single = itertools.product([1, 2], repeat=2)#[1,2]x[1,2] ->Single: [(1, 1), (1, 2), (2, 1), (2, 2)] repeat 3->Single: [(1, 1, 1), (1, 1, 2), (1, 2, 1), (1, 2, 2), (2, 1, 1), (2, 1, 2), (2, 2, 1), (2, 2, 2)]
single2 = itertools.product([1, 2], [1, 2]) # same as repeat 2
print("Single: ", list(single))
print("single 2", list(single2))
# product of two list a 2x2 lis by iterator list function
multiple = itertools.product([1, 2], ["a", "b"])#create iterator over lists and method product makes cartesian product
print("Multiple:", list(multiple))
# Example 13
# combinations with other values except hisself with list function position is important
it = itertools.permutations([1, 2, 3, 4], 2)#create iterator then method permutations
#combine element with succesive elements ->[(1, 2), (1, 3), (1, 4), (2, 1), (2, 3), (2, 4), (3, 1), (3, 2), (3, 4), (4, 1), (4, 2), (4, 3)]
original_print = print
print = pprint#change to pprint and back
print(list(it))
print = original_print
# Example 14
# combinations with other values except hisself with list function position is not important
# take values out of list
it = itertools.combinations([1, 2, 3, 4], 2)#[(1, 2), (1, 3), (1, 4), (2, 3), (2, 4), (3, 4)] don't replace item in stack
print(list(it))
# Example 15
# all combinations possible with full list
it = itertools.combinations_with_replacement([1, 2, 3, 4], 2)#iterator then method combinations is permutions where place in list is not important
original_print = print
print = pprint
print(list(it))#[(1, 1), (1, 2), (1, 3), (1, 4), (2, 2), (2, 3), (2, 4), (3, 3), (3, 4), (4, 4)]#combine with self and succesive others replace item to stack
print = original_print