effectivepython/example_code/item_52.py at master · sharc007/effectivepython · GitHub

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#!/usr/bin/env PYTHONHASHSEED=1234 python3

# 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 subprocess

# Enable these lines to make this example work on Windows

# import os

# os.environ['COMSPEC'] = 'powershell'

result = subprocess.run(

['echo', 'Hello from the child!'],

capture_output=True,

# Enable this line to make this example work on Windows

# shell=True,

encoding='utf-8')

result.check_returncode() # No exception means it exited cleanly

print(result.stdout)

# Example 2

# Use this line instead to make this example work on Windows

# proc = subprocess.Popen(['sleep', '1'], shell=True)

proc = subprocess.Popen(['sleep', '1'])

while proc.poll() is None:

print('Working...')

# Some time-consuming work here

import time

time.sleep(0.3)

print('Exit status', proc.poll())

# Example 3

import time

start = time.time()

sleep_procs = []

for _ in range(10):

# Use this line instead to make this example work on Windows

# proc = subprocess.Popen(['sleep', '1'], shell=True)

proc = subprocess.Popen(['sleep', '1'])

sleep_procs.append(proc)

# Example 4

for proc in sleep_procs:

proc.communicate()

end = time.time()

delta = end - start

print(f'Finished in {delta:.3} seconds')

# Example 5

import os

# On Windows, after installing OpenSSL, you may need to

# alias it in your PowerShell path with a command like:

# $env:path = $env:path + ";C:\Program Files\OpenSSL-Win64\bin"

def run_encrypt(data):

env = os.environ.copy()

env['password'] = 'zf7ShyBhZOraQDdE/FiZpm/m/8f9X+M1'

proc = subprocess.Popen(

['openssl', 'enc', '-des3', '-pass', 'env:password'],

env=env,

stdin=subprocess.PIPE,

stdout=subprocess.PIPE)

proc.stdin.write(data)

proc.stdin.flush() # Ensure that the child gets input

return proc

# Example 6

procs = []

for _ in range(3):

data = os.urandom(10)

proc = run_encrypt(data)

procs.append(proc)

# Example 7

for proc in procs:

out, _ = proc.communicate()

print(out[-10:])

# Example 8

def run_hash(input_stdin):

return subprocess.Popen(

['openssl', 'dgst', '-whirlpool', '-binary'],

stdin=input_stdin,

stdout=subprocess.PIPE)

# Example 9

encrypt_procs = []

hash_procs = []

for _ in range(3):

data = os.urandom(100)

encrypt_proc = run_encrypt(data)

encrypt_procs.append(encrypt_proc)

hash_proc = run_hash(encrypt_proc.stdout)

hash_procs.append(hash_proc)

# Ensure that the child consumes the input stream and

# the communicate() method doesn't inadvertently steal

# input from the child. Also lets SIGPIPE propagate to

# the upstream process if the downstream process dies.

encrypt_proc.stdout.close()

encrypt_proc.stdout = None

# Example 10

for proc in encrypt_procs:

proc.communicate()

assert proc.returncode == 0

for proc in hash_procs:

out, _ = proc.communicate()

print(out[-10:])

assert proc.returncode == 0

# Example 11

# Use this line instead to make this example work on Windows

# proc = subprocess.Popen(['sleep', '10'], shell=True)

proc = subprocess.Popen(['sleep', '10'])

try:

proc.communicate(timeout=0.1)

except subprocess.TimeoutExpired:

proc.terminate()

proc.wait()

print('Exit status', proc.poll())

effectivepython/example_code/item_52.py at master · sharc007/effectivepython · GitHub

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