Python standard library: os

dir(os)

dir(os) finds the following «members» of os:

`abc`
`abort()`
`access()`
`altsep`
`chdir()`	Changes the working directory to a given path or file descriptor. See also `fchdir()`, `getcwd()`.
`_check_methods()`
`chmod()`
`chown()`
`chroot()`
`CLD_CONTINUED`
`CLD_DUMPED`
`CLD_EXITED`
`CLD_KILLED`
`CLD_STOPPED`
`CLD_TRAPPED`
`close()`
`closerange()`
`confstr()`
`confstr_names`
`copy_file_range()`
`cpu_count()`
`ctermid()`	Filename of the controlling process's terminal (for example `/dev/tty`)
`curdir`
`defpath`
`device_encoding()`
`devnull`
`DirEntry`
`dup()`
`dup2()`
`_Environ`
`environ`
`environb`
`error`
`EX_CANTCREAT`
`EX_CONFIG`
`EX_DATAERR`
`execl()`
`execle()`
`execlp()`
`execlpe()`
`execv()`
`execve()`
`execvp()`
`_execvpe()`
`execvpe()`
`EX_IOERR`
`_exists()`
`_exit()`	Exit the process with a given status and without calling cleanup handlers registered with `atexit`. The standard way to quit from a process is `sys.exit()`. `os_exit()` should normally be used in the child process after a `fork()`.
`EX_NOHOST`
`EX_NOINPUT`
`EX_NOPERM`
`EX_NOUSER`
`EX_OK`
`EX_OSERR`
`EX_OSFILE`
`EX_PROTOCOL`
`EX_SOFTWARE`
`EX_TEMPFAIL`
`extsep`
`EX_UNAVAILABLE`
`EX_USAGE`
`fchdir()`
`fchmod()`
`fchown()`
`fdatasync()`
`fdopen()`
`F_LOCK`
`F_OK`
`fork()`
`forkpty()`
`fpathconf()`
`fsdecode()`
`fsencode()`
`_fspath()`
`fspath()`
`fstat()`
`fstatvfs()`
`fsync()`
`F_TEST`
`F_TLOCK`
`ftruncate()`
`F_ULOCK`
`_fwalk()`
`fwalk()`
`GenericAlias`
`get_blocking()`
`getcwd()`
`getcwdb()`
`getegid()`
`getenv()`
`getenvb()`
`geteuid()`
`get_exec_path()`
`_get_exports_list()`
`getgid()`
`getgrouplist()`
`getgroups()`
`get_inheritable()`
`getloadavg()`
`getlogin()`
`getpgid()`
`getpgrp()`
`getpid()`
`getppid()`
`getpriority()`
`getrandom()`
`getresgid()`
`getresuid()`
`getsid()`
`get_terminal_size()`
`getuid()`
`getxattr()`
`GRND_NONBLOCK`
`GRND_RANDOM`
`initgroups()`
`isatty()`
`kill()`
`killpg()`
`lchown()`
`linesep`
`link()`
`listdir()`	The list of filenames found in the specified directory (default is `'.'`). Compare with `scandir()`.
`listxattr()`
`lockf()`
`lseek()`
`lstat()`
`major()`
`makedev()`
`makedirs()`
`Mapping`
`memfd_create()`
`MFD_ALLOW_SEALING`
`MFD_CLOEXEC`
`MFD_HUGE_16GB`
`MFD_HUGE_16MB`
`MFD_HUGE_1GB`
`MFD_HUGE_1MB`
`MFD_HUGE_256MB`
`MFD_HUGE_2GB`
`MFD_HUGE_2MB`
`MFD_HUGE_32MB`
`MFD_HUGE_512KB`
`MFD_HUGE_512MB`
`MFD_HUGE_64KB`
`MFD_HUGE_8MB`
`MFD_HUGE_MASK`
`MFD_HUGE_SHIFT`
`MFD_HUGETLB`
`minor()`
`mkdir()`
`mkfifo()`
`mknod()`
`MutableMapping`
`name`	The name of the operating system module (one of `posix`, `nt`, `java`). Compare with `uname()` and `sys.platform`
`NGROUPS_MAX`
`nice()`
`O_ACCMODE`
`O_APPEND`
`O_ASYNC`
`O_CLOEXEC`
`O_CREAT`
`O_DIRECT`
`O_DIRECTORY`
`O_DSYNC`
`O_EXCL`
`O_LARGEFILE`
`O_NDELAY`
`O_NOATIME`
`O_NOCTTY`
`O_NOFOLLOW`
`O_NONBLOCK`
`O_PATH`
`open()`
`openpty()`
`O_RDONLY`
`O_RDWR`
`O_RSYNC`
`O_SYNC`
`O_TMPFILE`
`O_TRUNC`
`O_WRONLY`
`P_ALL`
`pardir`
`path`
`pathconf()`
`pathconf_names`
`PathLike`
`pathsep`
`pidfd_open()`
`pipe()`
`pipe2()`
`P_NOWAIT`
`P_NOWAITO`
`popen()`
`POSIX_FADV_DONTNEED`
`posix_fadvise()`
`POSIX_FADV_NOREUSE`
`POSIX_FADV_NORMAL`
`POSIX_FADV_RANDOM`
`POSIX_FADV_SEQUENTIAL`
`POSIX_FADV_WILLNEED`
`posix_fallocate()`
`posix_spawn()`
`POSIX_SPAWN_CLOSE`
`POSIX_SPAWN_DUP2`
`POSIX_SPAWN_OPEN`
`posix_spawnp()`
`P_PGID`
`P_PID`
`P_PIDFD`
`pread()`
`preadv()`
`PRIO_PGRP`
`PRIO_PROCESS`
`PRIO_USER`
`putenv()`
`P_WAIT`
`pwrite()`
`pwritev()`
`read()`
`readlink()`
`readv()`
`register_at_fork()`
`remove()`
`removedirs()`
`removexattr()`
`rename()`
`renames()`
`replace()`
`rmdir()`
`R_OK`
`RTLD_DEEPBIND`
`RTLD_GLOBAL`
`RTLD_LAZY`
`RTLD_LOCAL`
`RTLD_NODELETE`
`RTLD_NOLOAD`
`RTLD_NOW`
`RWF_DSYNC`
`RWF_HIPRI`
`RWF_NOWAIT`
`RWF_SYNC`
`scandir()`	Similar to `listdir()` but returns an iterator which returns `posic.DirEntry` objects. See also the shell command `ls`.
`SCHED_BATCH`
`SCHED_FIFO`
`sched_getaffinity()`
`sched_getparam()`
`sched_get_priority_max()`
`sched_get_priority_min()`
`sched_getscheduler()`
`SCHED_IDLE`
`SCHED_OTHER`
`sched_param`
`SCHED_RESET_ON_FORK`
`SCHED_RR`
`sched_rr_get_interval()`
`sched_setaffinity()`
`sched_setparam()`
`sched_setscheduler()`
`sched_yield()`
`SEEK_CUR`
`SEEK_DATA`
`SEEK_END`
`SEEK_HOLE`
`SEEK_SET`
`sendfile()`
`sep`
`set_blocking()`
`setegid()`
`seteuid()`
`setgid()`
`setgroups()`
`set_inheritable()`
`setpgid()`
`setpgrp()`
`setpriority()`
`setregid()`
`setresgid()`
`setresuid()`
`setreuid()`
`setsid()`
`setuid()`
`setxattr()`
`spawnl()`
`spawnle()`
`spawnlp()`
`spawnlpe()`
`spawnv()`
`spawnve()`
`_spawnvef()`
`spawnvp()`
`spawnvpe()`
`st`
`ST_APPEND`
`stat()`
`stat_result`
`statvfs()`
`statvfs_result`
`ST_MANDLOCK`
`ST_NOATIME`
`ST_NODEV`
`ST_NODIRATIME`
`ST_NOEXEC`
`ST_NOSUID`
`ST_RDONLY`
`ST_RELATIME`
`strerror()`
`ST_SYNCHRONOUS`
`ST_WRITE`
`supports_bytes_environ`
`supports_dir_fd`
`supports_effective_ids`
`supports_fd`
`supports_follow_symlinks`
`symlink()`
`sync()`
`sys`
`sysconf()`
`sysconf_names`
`system()`
`tcgetpgrp()`
`tcsetpgrp()`
`terminal_size`
`times()`
`times_result`
`TMP_MAX`
`truncate()`
`ttyname()`
`umask()`
`uname()`	See also `os.name`, the `platform` module and the shell command `uname`.
`uname_result`
`unlink()`
`unsetenv()`
`urandom()`
`utime()`
`wait()`
`wait3()`
`wait4()`
`waitid()`
`waitid_result`
`waitpid()`
`waitstatus_to_exitcode()`
`_walk()`
`walk()`
`WCONTINUED`
`WCOREDUMP()`
`WEXITED`
`WEXITSTATUS()`
`WIFCONTINUED()`
`WIFEXITED()`
`WIFSIGNALED()`
`WIFSTOPPED()`
`WNOHANG`
`WNOWAIT`
`W_OK`
`_wrap_close`
`write()`
`writev()`
`WSTOPPED`
`WSTOPSIG()`
`WTERMSIG()`
`WUNTRACED`
`XATTR_CREATE`
`XATTR_REPLACE`
`XATTR_SIZE_MAX`
`X_OK`

Iterating over files and directory (os.listdir, os.scandir)

The functions os.listdir and os.scandir both allow to iterate (non-recursively) over files and directories in a given directory.

The functionality os.listdir() was improved by os.scandir().

As per PEP 0471, using os.scandir() can improve the performance.

os.listdir() returns bare filename strings.

os.scandir() returns DirEntry objects which also allow to query additional data for the individual files/directories, such as

name (Compare with sys.platform)
path
inode()
is_dir(…)
is_file(…)
is_symlink(…)
stat(…)

Both, os.listdir() and os.scandir() skip the special directory entries . and ...

os.walk() might be used to iterate recursively.

Remove files and directories

Although Python has a built-in function to create files (open()), it does not have a built-in function to remove them. The functionality to remove files (and directories) is found in os:

os.remove()
os.removedirs()
os.rmdir()

In order to remove an entire directory tree, shutil.rmtree() can be used.

Note that the functions to check the existence of files and directories are located in the standard library os.path.

Create directories

The functions to create directories are

os.mkdir()
os.makedirs()

Print environment variables

The following script uses os.environ to print the environment variables that are defined in the current session.

Because the PATH environment variable is somewhat special because it consists of multiple paths, the script uses sys.path to print the list of directories that are searched for when trying to import a module.

import os
import sys

print("Defined environment variables:")
for var in os.environ:
    if var == 'PATH':
       sys.stdout.write ("  %-25s = " % var)
       path_iter = iter(sys.path)
       print(next(path_iter))  # print 1st path on same line as "PATH...="
       for dir in path_iter:   # print other paths indented:
           print((' ' * 30) + dir)
    else:
       print("  %-25s = %s  " % (var, os.environ[var]))

print('')
print("Expanded $HOME")
print("  " + os.path.expandvars('$HOME'))

Github repository about-python, path: /standard-library/os/environ.py

system

os.system(cmd) executes cmd in a subshell, using the standard C function system().

Consider replacing using os.system with functions found in the standard library module subprocess.