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item_024.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")
import itertools
print("Example 2")
it = itertools.chain([1, 2, 3], [4, 5, 6])
print(list(it))
print("Example 3")
it1 = [i * 3 for i in ("a", "b", "c")]
it2 = [j * 2 for j in ("x", "y", "z")]
nested_it = [it1, it2]
output_it = itertools.chain.from_iterable(nested_it)
print(list(output_it))
print("Example 4")
it = itertools.repeat("hello", 3)
print(list(it))
print("Example 5")
it = itertools.cycle([1, 2])
result = [next(it) for _ in range(10)]
print(result)
print("Example 6")
it1, it2, it3 = itertools.tee(["first", "second"], 3)
print(list(it1))
print(list(it2))
print(list(it3))
print("Example 7")
keys = ["one", "two", "three"]
values = [1, 2]
normal = list(zip(keys, values))
print("zip: ", normal)
it = itertools.zip_longest(keys, values, fillvalue="nope")
longest = list(it)
print("zip_longest:", longest)
print("Example 8")
values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
first_five = itertools.islice(values, 5)
print("First five: ", list(first_five))
middle_odds = itertools.islice(values, 2, 8, 2)
print("Middle odds:", list(middle_odds))
print("Example 9")
values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
less_than_seven = lambda x: x < 7
it = itertools.takewhile(less_than_seven, values)
print(list(it))
print("Example 10")
values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
less_than_seven = lambda x: x < 7
it = itertools.dropwhile(less_than_seven, values)
print(list(it))
print("Example 11")
values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
evens = lambda x: x % 2 == 0
filter_result = filter(evens, values)
print("Filter: ", list(filter_result))
filter_false_result = itertools.filterfalse(evens, values)
print("Filter false:", list(filter_false_result))
print("Example 12")
it = itertools.batched([1, 2, 3, 4, 5, 6, 7, 8, 9], 3)
print(list(it))
print("Example 13")
it = itertools.batched([1, 2, 3], 2)
print(list(it))
print("Example 14")
route = ["Los Angeles", "Bakersfield", "Modesto", "Sacramento"]
it = itertools.pairwise(route)
print(list(it))
print("Example 15")
values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
sum_reduce = itertools.accumulate(values)
print("Sum: ", list(sum_reduce))
def sum_modulo_20(first, second):
output = first + second
return output % 20
modulo_reduce = itertools.accumulate(values, sum_modulo_20)
print("Modulo:", list(modulo_reduce))
print("Example 16")
single = itertools.product([1, 2], repeat=2)
print("Single: ", list(single))
multiple = itertools.product([1, 2], ["a", "b"])
print("Multiple:", list(multiple))
print("Example 17")
it = itertools.permutations([1, 2, 3, 4], 2)
original_print = print
print = pprint
print(list(it))
print = original_print
print("Example 18")
it = itertools.combinations([1, 2, 3, 4], 2)
print(list(it))
print("Example 19")
it = itertools.combinations_with_replacement([1, 2, 3, 4], 2)
original_print = print
print = pprint
print(list(it))
print = original_print