item_36.py

#!/usr/bin/env python3

# Copyright 2014 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.

# Preamble to mimick book environment
import logging
from pprint import pprint
from sys import stdout as STDOUT


# Example 1
import subprocess
proc = subprocess.Popen(
    ['echo', 'Hello from the child!'],
    stdout=subprocess.PIPE)
out, err = proc.communicate()
print(out.decode('utf-8'))


# Example 2
from time import sleep, time
proc = subprocess.Popen(['sleep', '0.3'])
while proc.poll() is None:
    print('Working...')
    # Some time consuming work here
    sleep(0.2)

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


# Example 3
def run_sleep(period):
    proc = subprocess.Popen(['sleep', str(period)])
    return proc

start = time()
procs = []
for _ in range(10):
    proc = run_sleep(0.1)
    procs.append(proc)


# Example 4
for proc in procs:
    proc.communicate()
end = time()
print('Finished in %.3f seconds' % (end - start))


# Example 5
import os

def run_openssl(data):
    env = os.environ.copy()
    env['password'] = b'\xe24U\n\xd0Ql3S\x11'
    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 the child gets input
    return proc


# Example 6
import os
procs = []
for _ in range(3):
    data = os.urandom(10)
    proc = run_openssl(data)
    procs.append(proc)


# Example 7
for proc in procs:
    out, err = proc.communicate()
    print(out[-10:])


# Example 8
def run_md5(input_stdin):
    proc = subprocess.Popen(
        ['md5'],
        stdin=input_stdin,
        stdout=subprocess.PIPE)
    return proc


# Example 9
input_procs = []
hash_procs = []
for _ in range(3):
    data = os.urandom(10)
    proc = run_openssl(data)
    input_procs.append(proc)
    hash_proc = run_md5(proc.stdout)
    hash_procs.append(hash_proc)


# Example 10
for proc in input_procs:
    proc.communicate()
for proc in hash_procs:
    out, err = proc.communicate()
    print(out.strip())


# Example 11
proc = run_sleep(10)
try:
    proc.communicate(timeout=0.1)
except subprocess.TimeoutExpired:
    proc.terminate()
    proc.wait()

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