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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 normalize(numbers):
total = sum(numbers)
result = []
for value in numbers:
percent = 100 * value / total
result.append(percent)
return result
# Example 2
visits = [15, 35, 80]
percentages = normalize(visits)
print(percentages)
assert sum(percentages) == 100.0
# Example 3
path = 'my_numbers.txt'
with open(path, 'w') as f:
for i in (15, 35, 80):
f.write('%d\n' % i)
def read_visits(data_path):
with open(data_path) as f:
for line in f:
yield int(line)
# Example 4
it = read_visits('my_numbers.txt')
percentages = normalize(it)
print(percentages)
# Example 5
it = read_visits('my_numbers.txt')
print(list(it))
print(list(it)) # Already exhausted
# Example 6
def normalize_copy(numbers):
numbers_copy = list(numbers) # Copy the iterator
total = sum(numbers_copy)
result = []
for value in numbers_copy:
percent = 100 * value / total
result.append(percent)
return result
# Example 7
it = read_visits('my_numbers.txt')
percentages = normalize_copy(it)
print(percentages)
assert sum(percentages) == 100.0
# Example 8
def normalize_func(get_iter):
total = sum(get_iter()) # New iterator
result = []
for value in get_iter(): # New iterator
percent = 100 * value / total
result.append(percent)
return result
# Example 9
path = 'my_numbers.txt'
percentages = normalize_func(lambda: read_visits(path))
print(percentages)
assert sum(percentages) == 100.0
# Example 10
class ReadVisits:
def __init__(self, data_path):
self.data_path = data_path
def __iter__(self):
with open(self.data_path) as f:
for line in f:
yield int(line)
# Example 11
visits = ReadVisits(path)
percentages = normalize(visits)
print(percentages)
assert sum(percentages) == 100.0
# Example 12
def normalize_defensive(numbers):
if iter(numbers) is numbers: # An iterator -- bad!
raise TypeError('Must supply a container')
total = sum(numbers)
result = []
for value in numbers:
percent = 100 * value / total
result.append(percent)
return result
visits = [15, 35, 80]
normalize_defensive(visits) # No error
it = iter(visits)
try:
normalize_defensive(it)
except TypeError:
pass
else:
assert False
# Example 13
from collections.abc import Iterator
def normalize_defensive(numbers):
if isinstance(numbers, Iterator): # Another way to check
raise TypeError('Must supply a container')
total = sum(numbers)
result = []
for value in numbers:
percent = 100 * value / total
result.append(percent)
return result
visits = [15, 35, 80]
normalize_defensive(visits) # No error
it = iter(visits)
try:
normalize_defensive(it)
except TypeError:
pass
else:
assert False
# Example 14
visits = [15, 35, 80]
percentages = normalize_defensive(visits)
assert sum(percentages) == 100.0
visits = ReadVisits(path)
percentages = normalize_defensive(visits)
assert sum(percentages) == 100.0
# Example 15
try:
visits = [15, 35, 80]
it = iter(visits)
normalize_defensive(it)
except:
logging.exception('Expected')
else:
assert False