os — 特定操作系统的具体配置

Examining the File System Contents

# os_listdir.py
import os
import sys

print(sorted(os.listdir(sys.argv[1])))

# os_walk.py
import os
import sys

# If we are not given a path to list, use /tmp
if len(sys.argv) == 1:
    root = '/tmp'
else:
    root = sys.argv[1]

for dir_name, sub_dirs, files in os.walk(root):
    print(dir_name)
    # Make the subdirectory names stand out with /
    sub_dirs = [n + '/' for n in sub_dirs]
    # Mix the directory contents together
    contents = sub_dirs + files
    contents.sort()
    # Show the contents
    for c in contents:
        print('  {}'.format(c))
    print()

# os_scandir.py
import os
import sys

for entry in os.scandir(sys.argv[1]):
    if entry.is_dir():
        typ = 'dir'
    elif entry.is_file():
        typ = 'file'
    elif entry.is_symlink():
        typ = 'link'
    else:
        typ = 'unknown'
    print('{name} {typ}'.format(
        name=entry.name,
        typ=typ,
    ))

Managing File System Permissions

# os_stat.py
import os
import sys
import time

if len(sys.argv) == 1:
    filename = __file__
else:
    filename = sys.argv[1]

stat_info = os.stat(filename)

print('os.stat({}):'.format(filename))
print('  Size:', stat_info.st_size)
print('  Permissions:', oct(stat_info.st_mode))
print('  Owner:', stat_info.st_uid)
print('  Device:', stat_info.st_dev)
print('  Created      :', time.ctime(stat_info.st_ctime))
print('  Last modified:', time.ctime(stat_info.st_mtime))
print('  Last accessed:', time.ctime(stat_info.st_atime))

# os_stat_chmod.py
import os
import stat

filename = 'os_stat_chmod_example.txt'
if os.path.exists(filename):
    os.unlink(filename)
with open(filename, 'wt') as f:
    f.write('contents')

# Determine what permissions are already set using stat
existing_permissions = stat.S_IMODE(os.stat(filename).st_mode)

if not os.access(filename, os.X_OK):
    print('Adding execute permission')
    new_permissions = existing_permissions | stat.S_IXUSR
else:
    print('Removing execute permission')
    # use xor to remove the user execute permission
    new_permissions = existing_permissions ^ stat.S_IXUSR

os.chmod(filename, new_permissions)

# os_access.py
import os

print('Testing:', __file__)
print('Exists:', os.access(__file__, os.F_OK))
print('Readable:', os.access(__file__, os.R_OK))
print('Writable:', os.access(__file__, os.W_OK))
print('Executable:', os.access(__file__, os.X_OK))

Creating and Deleting Directories

# os_directories.py
import os

dir_name = 'os_directories_example'

print('Creating', dir_name)
os.makedirs(dir_name)

file_name = os.path.join(dir_name, 'example.txt')
print('Creating', file_name)
with open(file_name, 'wt') as f:
    f.write('example file')

print('Cleaning up')
os.unlink(file_name)
os.rmdir(dir_name)

Working with Symbolic Links

# os_symlinks.py
import os

link_name = '/tmp/' + os.path.basename(__file__)

print('Creating link {} -> {}'.format(link_name, __file__))
os.symlink(__file__, link_name)

stat_info = os.lstat(link_name)
print('Permissions:', oct(stat_info.st_mode))

print('Points to:', os.readlink(link_name))

# Cleanup
os.unlink(link_name)

Safely Replacing an Existing File

# os_rename_replace.py
import glob
import os


with open('rename_start.txt', 'w') as f:
    f.write('starting as rename_start.txt')

print('Starting:', glob.glob('rename*.txt'))

os.rename('rename_start.txt', 'rename_finish.txt')

print('After rename:', glob.glob('rename*.txt'))

with open('rename_finish.txt', 'r') as f:
    print('Contents:', repr(f.read()))

with open('rename_new_contents.txt', 'w') as f:
    f.write('ending with contents of rename_new_contents.txt')

os.replace('rename_new_contents.txt', 'rename_finish.txt')

with open('rename_finish.txt', 'r') as f:
    print('After replace:', repr(f.read()))

for name in glob.glob('rename*.txt'):
    os.unlink(name)

Detecting and Changing the Process Owner

# os_process_user_example.py
import os

TEST_GID = 502
TEST_UID = 502


def show_user_info():
    print('User (actual/effective)  : {} / {}'.format(
        os.getuid(), os.geteuid()))
    print('Group (actual/effective) : {} / {}'.format(
        os.getgid(), os.getegid()))
    print('Actual Groups   :', os.getgroups())


print('BEFORE CHANGE:')
show_user_info()
print()

try:
    os.setegid(TEST_GID)
except OSError:
    print('ERROR: Could not change effective group. '
          'Rerun as root.')
else:
    print('CHANGE GROUP:')
    show_user_info()
    print()

try:
    os.seteuid(TEST_UID)
except OSError:
    print('ERROR: Could not change effective user. '
          'Rerun as root.')
else:
    print('CHANGE USER:')
    show_user_info()
    print()

Managing the Process Environment

# os_environ_example.py
import os

print('Initial value:', os.environ.get('TESTVAR', None))
print('Child process:')
os.system('echo $TESTVAR')

os.environ['TESTVAR'] = 'THIS VALUE WAS CHANGED'

print()
print('Changed value:', os.environ['TESTVAR'])
print('Child process:')
os.system('echo $TESTVAR')

del os.environ['TESTVAR']

print()
print('Removed value:', os.environ.get('TESTVAR', None))
print('Child process:')
os.system('echo $TESTVAR')

Managing the Process Working Directory

# os_cwd_example.py
import os

print('Starting:', os.getcwd())

print('Moving up one:', os.pardir)
os.chdir(os.pardir)

print('After move:', os.getcwd())

Running External Commands

# os_system_example.py
import os

# Simple command
os.system('pwd')

# os_system_background.py
import os
import time

print('Calling...')
os.system('date; (sleep 3; date) &')

print('Sleeping...')
time.sleep(5)

Creating Processes with os.fork()

# os_fork_example.py
import os

pid = os.fork()

if pid:
    print('Child process id:', pid)
else:
    print('I am the child')

# os_kill_example.py
import os
import signal
import time


def signal_usr1(signum, frame):
    "Callback invoked when a signal is received"
    pid = os.getpid()
    print('Received USR1 in process {}'.format(pid))


print('Forking...')
child_pid = os.fork()
if child_pid:
    print('PARENT: Pausing before sending signal...')
    time.sleep(1)
    print('PARENT: Signaling {}'.format(child_pid))
    os.kill(child_pid, signal.SIGUSR1)
else:
    print('CHILD: Setting up signal handler')
    signal.signal(signal.SIGUSR1, signal_usr1)
    print('CHILD: Pausing to wait for signal')
    time.sleep(5)

# os_exec_example.py
import os

child_pid = os.fork()
if child_pid:
    os.waitpid(child_pid, 0)
else:
    os.execlp('pwd', 'pwd', '-P')

Waiting for Child Processes

# os_wait_example.py
import os
import sys
import time

for i in range(2):
    print('PARENT {}: Forking {}'.format(os.getpid(), i))
    worker_pid = os.fork()
    if not worker_pid:
        print('WORKER {}: Starting'.format(i))
        time.sleep(2 + i)
        print('WORKER {}: Finishing'.format(i))
        sys.exit(i)

for i in range(2):
    print('PARENT: Waiting for {}'.format(i))
    done = os.wait()
    print('PARENT: Child done:', done)

# os_waitpid_example.py
import os
import sys
import time

workers = []
for i in range(2):
    print('PARENT {}: Forking {}'.format(os.getpid(), i))
    worker_pid = os.fork()
    if not worker_pid:
        print('WORKER {}: Starting'.format(i))
        time.sleep(2 + i)
        print('WORKER {}: Finishing'.format(i))
        sys.exit(i)
    workers.append(worker_pid)

for pid in workers:
    print('PARENT: Waiting for {}'.format(pid))
    done = os.waitpid(pid, 0)
    print('PARENT: Child done:', done)

Spawning New Processes

# os_spawn_example.py
import os

os.spawnlp(os.P_WAIT, 'pwd', 'pwd', '-P')

Operating System Error Codes

# os_strerror.py
import errno
import os

for num in [errno.ENOENT, errno.EINTR, errno.EBUSY]:
    name = errno.errorcode[num]
    print('[{num:>2}] {name:<6}: {msg}'.format(
        name=name, num=num, msg=os.strerror(num)))