subprocess --- 子行程管理¶The subprocess module allows you to spawn new processes, connect to their
input/output/error pipes, and obtain their return codes. This module intends to
replace several older modules and functions:
os.system
os.spawn*
Information about how the subprocess module can be used to replace these
modules and functions can be found in the following sections.
也參考
PEP 324 -- 提議 subprocess 模組的 PEP
適用: not Android, not iOS, not WASI.
此模組在行動平台或WebAssembly 平台上不支援。
subprocess Module¶The recommended approach to invoking subprocesses is to use the run()
function for all use cases it can handle. For more advanced use cases, the
underlying Popen interface can be used directly.
Run the command described by args. Wait for command to complete, then
return a CompletedProcess instance.
The arguments shown above are merely the most common ones, described below
in Frequently Used Arguments (hence the use of keyword-only notation
in the abbreviated signature). The full function signature is largely the
same as that of the Popen constructor - most of the arguments to
this function are passed through to that interface. (timeout, input,
check, and capture_output are not.)
If capture_output is true, stdout and stderr will be captured.
When used, the internal Popen object is automatically created with
stdout and stderr both set to PIPE.
The stdout and stderr arguments may not be supplied at the same time as capture_output.
If you wish to capture and combine both streams into one,
set stdout to PIPE
and stderr to STDOUT,
instead of using capture_output.
A timeout may be specified in seconds, it is internally passed on to
Popen.communicate(). If the timeout expires, the child process will be
killed and waited for. The TimeoutExpired exception will be
re-raised after the child process has terminated. The initial process
creation itself cannot be interrupted on many platform APIs so you are not
guaranteed to see a timeout exception until at least after however long
process creation takes.
The input argument is passed to Popen.communicate() and thus to the
subprocess's stdin. If used it must be a byte sequence, or a string if
encoding or errors is specified or text is true. When
used, the internal Popen object is automatically created with
stdin set to PIPE,
and the stdin argument may not be used as well.
If check is true, and the process exits with a non-zero exit code, a
CalledProcessError exception will be raised. Attributes of that
exception hold the arguments, the exit code, and stdout and stderr if they
were captured.
If encoding or errors are specified, or text is true,
file objects for stdin, stdout and stderr are opened in text mode using the
specified encoding and errors or the io.TextIOWrapper default.
The universal_newlines argument is equivalent to text and is provided
for backwards compatibility. By default, file objects are opened in binary mode.
If env is not None, it must be a mapping that defines the environment
variables for the new process; these are used instead of the default
behavior of inheriting the current process' environment. It is passed
directly to Popen. This mapping can be str to str on any platform
or bytes to bytes on POSIX platforms much like os.environ or
os.environb.
範例：
>>> subprocess.run(["ls", "-l"]) # 不捕捉輸出
CompletedProcess(args=['ls', '-l'], returncode=0)
>>> subprocess.run("exit 1", shell=True, check=True)
Traceback (most recent call last):
...
subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1
>>> subprocess.run(["ls", "-l", "/dev/null"], capture_output=True)
CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0,
stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n', stderr=b'')
在 3.5 版被加入.
在 3.6 版的變更: 新增 encoding 與 errors 參數。
在 3.7 版的變更: Added the text parameter, as a more understandable alias of universal_newlines. Added the capture_output parameter.
在 3.12 版的變更: Changed Windows shell search order for shell=True. The current
directory and %PATH% are replaced with %COMSPEC% and
%SystemRoot%\System32\cmd.exe. As a result, dropping a
malicious program named cmd.exe into a current directory no
longer works.
The return value from run(), representing a process that has finished.
The arguments used to launch the process. This may be a list or a string.
Exit status of the child process. Typically, an exit status of 0 indicates that it ran successfully.
A negative value -N indicates that the child was terminated by signal
N (POSIX only).
Captured stdout from the child process. A bytes sequence, or a string if
run() was called with an encoding, errors, or text=True.
None if stdout was not captured.
If you ran the process with stderr=subprocess.STDOUT, stdout and
stderr will be combined in this attribute, and stderr will be
None.
Captured stderr from the child process. A bytes sequence, or a string if
run() was called with an encoding, errors, or text=True.
None if stderr was not captured.
If returncode is non-zero, raise a CalledProcessError.
在 3.5 版被加入.
Special value that can be used as the stdin, stdout or stderr argument
to Popen and indicates that the special file os.devnull
will be used.
在 3.3 版被加入.
Special value that can be used as the stdin, stdout or stderr argument
to Popen and indicates that a pipe to the standard stream should be
opened. Most useful with Popen.communicate().
Special value that can be used as the stderr argument to Popen and
indicates that standard error should go into the same handle as standard
output.
Base class for all other exceptions from this module.
在 3.3 版被加入.
Subclass of SubprocessError, raised when a timeout expires
while waiting for a child process.
Command that was used to spawn the child process.
Timeout in seconds.
Output of the child process if it was captured by run() or
check_output(). Otherwise, None. This is always
bytes when any output was captured regardless of the
text=True setting. It may remain None instead of b''
when no output was observed.
Stderr output of the child process if it was captured by run().
Otherwise, None. This is always bytes when stderr output
was captured regardless of the text=True setting. It may remain
None instead of b'' when no stderr output was observed.
在 3.3 版被加入.
在 3.5 版的變更: stdout and stderr attributes added
Subclass of SubprocessError, raised when a process run by
check_call(), check_output(), or run() (with check=True)
returns a non-zero exit status.
Exit status of the child process. If the process exited due to a signal, this will be the negative signal number.
Command that was used to spawn the child process.
Output of the child process if it was captured by run() or
check_output(). Otherwise, None.
在 3.5 版的變更: stdout and stderr attributes added
To support a wide variety of use cases, the Popen constructor (and
the convenience functions) accept a large number of optional arguments. For
most typical use cases, many of these arguments can be safely left at their
default values. The arguments that are most commonly needed are:
args is required for all calls and should be a string, or a sequence of program arguments. Providing a sequence of arguments is generally preferred, as it allows the module to take care of any required escaping and quoting of arguments (e.g. to permit spaces in file names). If passing a single string, either shell must be
True(see below) or else the string must simply name the program to be executed without specifying any arguments.stdin, stdout and stderr specify the executed program's standard input, standard output and standard error file handles, respectively. Valid values are
None,PIPE,DEVNULL, an existing file descriptor (a positive integer), and an existing file object with a valid file descriptor. With the default settings ofNone, no redirection will occur.PIPEindicates that a new pipe to the child should be created.DEVNULLindicates that the special fileos.devnullwill be used. Additionally, stderr can beSTDOUT, which indicates that the stderr data from the child process should be captured into the same file handle as for stdout.If encoding or errors are specified, or text (also known as universal_newlines) is true, the file objects stdin, stdout and stderr will be opened in text mode using the encoding and errors specified in the call or the defaults for
io.TextIOWrapper.For stdin, line ending characters
'\n'in the input will be converted to the default line separatoros.linesep. For stdout and stderr, all line endings in the output will be converted to'\n'. For more information see the documentation of theio.TextIOWrapperclass when the newline argument to its constructor isNone.If text mode is not used, stdin, stdout and stderr will be opened as binary streams. No encoding or line ending conversion is performed.
在 3.6 版的變更: 新增 encoding 與 errors 參數。
在 3.7 版的變更: Added the text parameter as an alias for universal_newlines.
備註
The newlines attribute of the file objects
Popen.stdin,Popen.stdoutandPopen.stderrare not updated by thePopen.communicate()method.If shell is
True, the specified command will be executed through the shell. This can be useful if you are using Python primarily for the enhanced control flow it offers over most system shells and still want convenient access to other shell features such as shell pipes, filename wildcards, environment variable expansion, and expansion of~to a user's home directory. However, note that Python itself offers implementations of many shell-like features (in particular,glob,fnmatch,os.walk(),os.path.expandvars(),os.path.expanduser(), andshutil).在 3.3 版的變更: When universal_newlines is
True, the class uses the encodinglocale.getpreferredencoding(False)instead oflocale.getpreferredencoding(). See theio.TextIOWrapperclass for more information on this change.備註
Read the Security Considerations section before using
shell=True.
These options, along with all of the other options, are described in more
detail in the Popen constructor documentation.
The underlying process creation and management in this module is handled by
the Popen class. It offers a lot of flexibility so that developers
are able to handle the less common cases not covered by the convenience
functions.
Execute a child program in a new process. On POSIX, the class uses
os.execvpe()-like behavior to execute the child program. On Windows,
the class uses the Windows CreateProcess() function. The arguments to
Popen are as follows.
args should be a sequence of program arguments or else a single string or path-like object. By default, the program to execute is the first item in args if args is a sequence. If args is a string, the interpretation is platform-dependent and described below. See the shell and executable arguments for additional differences from the default behavior. Unless otherwise stated, it is recommended to pass args as a sequence.
警告
For maximum reliability, use a fully qualified path for the executable.
To search for an unqualified name on PATH, use
shutil.which(). On all platforms, passing sys.executable
is the recommended way to launch the current Python interpreter again,
and use the -m command-line format to launch an installed module.
Resolving the path of executable (or the first item of args) is
platform dependent. For POSIX, see os.execvpe(), and note that
when resolving or searching for the executable path, cwd overrides the
current working directory and env can override the PATH
environment variable. For Windows, see the documentation of the
lpApplicationName and lpCommandLine parameters of WinAPI
CreateProcess, and note that when resolving or searching for the
executable path with shell=False, cwd does not override the
current working directory and env cannot override the PATH
environment variable. Using a full path avoids all of these variations.
An example of passing some arguments to an external program as a sequence is:
Popen(["/usr/bin/git", "commit", "-m", "Fixes a bug."])
On POSIX, if args is a string, the string is interpreted as the name or path of the program to execute. However, this can only be done if not passing arguments to the program.
備註
It may not be obvious how to break a shell command into a sequence of arguments,
especially in complex cases. shlex.split() can illustrate how to
determine the correct tokenization for args:
>>> import shlex, subprocess
>>> command_line = input()
/bin/vikings -input eggs.txt -output "spam spam.txt" -cmd "echo '$MONEY'"
>>> args = shlex.split(command_line)
>>> print(args)
['/bin/vikings', '-input', 'eggs.txt', '-output', 'spam spam.txt', '-cmd', "echo '$MONEY'"]
>>> p = subprocess.Popen(args) # 成功！
Note in particular that options (such as -input) and arguments (such as eggs.txt) that are separated by whitespace in the shell go in separate list elements, while arguments that need quoting or backslash escaping when used in the shell (such as filenames containing spaces or the echo command shown above) are single list elements.
On Windows, if args is a sequence, it will be converted to a string in a
manner described in Converting an argument sequence to a string on Windows. This is because
the underlying CreateProcess() operates on strings.
在 3.6 版的變更: args parameter accepts a path-like object if shell is
False and a sequence containing path-like objects on POSIX.
在 3.8 版的變更: args parameter accepts a path-like object if shell is
False and a sequence containing bytes and path-like objects
on Windows.
The shell argument (which defaults to False) specifies whether to use
the shell as the program to execute. If shell is True, it is
recommended to pass args as a string rather than as a sequence.
On POSIX with shell=True, the shell defaults to /bin/sh. If
args is a string, the string specifies the command
to execute through the shell. This means that the string must be
formatted exactly as it would be when typed at the shell prompt. This
includes, for example, quoting or backslash escaping filenames with spaces in
them. If args is a sequence, the first item specifies the command string, and
any additional items will be treated as additional arguments to the shell
itself. That is to say, Popen does the equivalent of:
Popen(['/bin/sh', '-c', args[0], args[1], ...])
On Windows with shell=True, the COMSPEC environment variable
specifies the default shell. The only time you need to specify
shell=True on Windows is when the command you wish to execute is built
into the shell (e.g. dir or copy). You do not need
shell=True to run a batch file or console-based executable.
備註
Read the Security Considerations section before using shell=True.
bufsize will be supplied as the corresponding argument to the
open() function when creating the stdin/stdout/stderr pipe
file objects:
0 means unbuffered (read and write are one
system call and can return short)
1 means line buffered
(only usable if text=True or universal_newlines=True)
any other positive value means use a buffer of approximately that size
negative bufsize (the default) means the system default of io.DEFAULT_BUFFER_SIZE will be used.
在 3.3.1 版的變更: bufsize now defaults to -1 to enable buffering by default to match the
behavior that most code expects. In versions prior to Python 3.2.4 and
3.3.1 it incorrectly defaulted to 0 which was unbuffered
and allowed short reads. This was unintentional and did not match the
behavior of Python 2 as most code expected.
The executable argument specifies a replacement program to execute. It
is very seldom needed. When shell=False, executable replaces the
program to execute specified by args. However, the original args is
still passed to the program. Most programs treat the program specified
by args as the command name, which can then be different from the program
actually executed. On POSIX, the args name
becomes the display name for the executable in utilities such as
ps. If shell=True, on POSIX the executable argument
specifies a replacement shell for the default /bin/sh.
在 3.6 版的變更: executable parameter accepts a path-like object on POSIX.
在 3.8 版的變更: executable parameter accepts a bytes and path-like object on Windows.
在 3.12 版的變更: Changed Windows shell search order for shell=True. The current
directory and %PATH% are replaced with %COMSPEC% and
%SystemRoot%\System32\cmd.exe. As a result, dropping a
malicious program named cmd.exe into a current directory no
longer works.
stdin, stdout and stderr specify the executed program's standard input,
standard output and standard error file handles, respectively. Valid values
are None, PIPE, DEVNULL, an existing file descriptor (a
positive integer), and an existing file object with a valid file
descriptor. With the default settings of None, no redirection will
occur. PIPE indicates that a new pipe to the child should be
created. DEVNULL indicates that the special file os.devnull
will be used. Additionally, stderr can be STDOUT, which indicates
that the stderr data from the applications should be captured into the same
file handle as for stdout.
If preexec_fn is set to a callable object, this object will be called in the child process just before the child is executed. (POSIX only)
警告
The preexec_fn parameter is NOT SAFE to use in the presence of threads in your application. The child process could deadlock before exec is called.
備註
If you need to modify the environment for the child use the env
parameter rather than doing it in a preexec_fn.
The start_new_session and process_group parameters should take the place of
code using preexec_fn to call os.setsid() or os.setpgid() in the child.
在 3.8 版的變更: The preexec_fn parameter is no longer supported in subinterpreters.
The use of the parameter in a subinterpreter raises
RuntimeError. The new restriction may affect applications that
are deployed in mod_wsgi, uWSGI, and other embedded environments.
If close_fds is true, all file descriptors except 0, 1 and
2 will be closed before the child process is executed. Otherwise
when close_fds is false, file descriptors obey their inheritable flag
as described in Inheritance of File Descriptors.
On Windows, if close_fds is true then no handles will be inherited by the
child process unless explicitly passed in the handle_list element of
STARTUPINFO.lpAttributeList, or by standard handle redirection.
在 3.2 版的變更: The default for close_fds was changed from False to
what is described above.
在 3.7 版的變更: On Windows the default for close_fds was changed from False to
True when redirecting the standard handles. It's now possible to
set close_fds to True when redirecting the standard handles.
pass_fds is an optional sequence of file descriptors to keep open
between the parent and child. Providing any pass_fds forces
close_fds to be True. (POSIX only)
在 3.2 版的變更: 新增 pass_fds 參數。
If cwd is not None, the function changes the working directory to
cwd before executing the child. cwd can be a string, bytes or
path-like object. On POSIX, the function
looks for executable (or for the first item in args) relative to cwd
if the executable path is a relative path.
在 3.6 版的變更: cwd parameter accepts a path-like object on POSIX.
在 3.7 版的變更: cwd parameter accepts a path-like object on Windows.
在 3.8 版的變更: cwd parameter accepts a bytes object on Windows.
If restore_signals is true (the default) all signals that Python has set to SIG_IGN are restored to SIG_DFL in the child process before the exec. Currently this includes the SIGPIPE, SIGXFZ and SIGXFSZ signals. (POSIX only)
在 3.2 版的變更: 新增 restore_signals。
If start_new_session is true the setsid() system call will be made in the
child process prior to the execution of the subprocess.
適用: POSIX
在 3.2 版的變更: 新增 start_new_session。
If process_group is a non-negative integer, the setpgid(0, value) system call will
be made in the child process prior to the execution of the subprocess.
適用: POSIX
在 3.11 版的變更: 新增 process_group。
If group is not None, the setregid() system call will be made in the
child process prior to the execution of the subprocess. If the provided
value is a string, it will be looked up via grp.getgrnam() and
the value in gr_gid will be used. If the value is an integer, it
will be passed verbatim. (POSIX only)
適用: POSIX
在 3.9 版被加入.
If extra_groups is not None, the setgroups() system call will be
made in the child process prior to the execution of the subprocess.
Strings provided in extra_groups will be looked up via
grp.getgrnam() and the values in gr_gid will be used.
Integer values will be passed verbatim. (POSIX only)
適用: POSIX
在 3.9 版被加入.
If user is not None, the setreuid() system call will be made in the
child process prior to the execution of the subprocess. If the provided
value is a string, it will be looked up via pwd.getpwnam() and
the value in pw_uid will be used. If the value is an integer, it will
be passed verbatim. (POSIX only)
適用: POSIX
在 3.9 版被加入.
If umask is not negative, the umask() system call will be made in the child process prior to the execution of the subprocess.
適用: POSIX
在 3.9 版被加入.
If env is not None, it must be a mapping that defines the environment
variables for the new process; these are used instead of the default
behavior of inheriting the current process' environment. This mapping can be
str to str on any platform or bytes to bytes on POSIX platforms much like
os.environ or os.environb.
備註
If specified, env must provide any variables required for the program to
execute. On Windows, in order to run a side-by-side assembly the
specified env must include a valid SystemRoot.
If encoding or errors are specified, or text is true, the file objects stdin, stdout and stderr are opened in text mode with the specified encoding and errors, as described above in Frequently Used Arguments. The universal_newlines argument is equivalent to text and is provided for backwards compatibility. By default, file objects are opened in binary mode.
在 3.6 版被加入: 新增 encoding 與 errors。
在 3.7 版被加入: text was added as a more readable alias for universal_newlines.
If given, startupinfo will be a STARTUPINFO object, which is
passed to the underlying CreateProcess function.
If given, creationflags, can be one or more of the following flags:
pipesize can be used to change the size of the pipe when
PIPE is used for stdin, stdout or stderr. The size of the pipe
is only changed on platforms that support this (only Linux at this time of
writing). Other platforms will ignore this parameter.
在 3.10 版的變更: 新增 pipesize 參數。
Popen objects are supported as context managers via the with statement:
on exit, standard file descriptors are closed, and the process is waited for.
with Popen(["ifconfig"], stdout=PIPE) as proc:
log.write(proc.stdout.read())
Popen and the other functions in this module that use it raise an
auditing event subprocess.Popen with arguments
executable, args, cwd, and env. The value for args
may be a single string or a list of strings, depending on platform.
在 3.2 版的變更: 新增情境管理器的支援。
在 3.6 版的變更: Popen destructor now emits a ResourceWarning warning if the child
process is still running.
在 3.8 版的變更: Popen can use os.posix_spawn() in some cases for better
performance. On Windows Subsystem for Linux and QEMU User Emulation,
Popen constructor using os.posix_spawn() no longer raise an
exception on errors like missing program, but the child process fails
with a non-zero returncode.
Exceptions raised in the child process, before the new program has started to execute, will be re-raised in the parent.
The most common exception raised is OSError. This occurs, for example,
when trying to execute a non-existent file. Applications should prepare for
OSError exceptions. Note that, when shell=True, OSError
will be raised by the child only if the selected shell itself was not found.
To determine if the shell failed to find the requested application, it is
necessary to check the return code or output from the subprocess.
A ValueError will be raised if Popen is called with invalid
arguments.
check_call() and check_output() will raise
CalledProcessError if the called process returns a non-zero return
code.
All of the functions and methods that accept a timeout parameter, such as
run() and Popen.communicate() will raise TimeoutExpired if
the timeout expires before the process exits.
Exceptions defined in this module all inherit from SubprocessError.
在 3.3 版被加入: The SubprocessError base class was added.
Unlike some other popen functions, this library will not
implicitly choose to call a system shell. This means that all characters,
including shell metacharacters, can safely be passed to child processes.
If the shell is invoked explicitly, via shell=True, it is the application's
responsibility to ensure that all whitespace and metacharacters are
quoted appropriately to avoid
shell injection
vulnerabilities. On some platforms, it is possible
to use shlex.quote() for this escaping.
On Windows, batch files (*.bat or *.cmd) may be launched by the
operating system in a system shell regardless of the arguments passed to this
library. This could result in arguments being parsed according to shell rules,
but without any escaping added by Python. If you are intentionally launching a
batch file with arguments from untrusted sources, consider passing
shell=True to allow Python to escape special characters. See gh-114539
for additional discussion.
Instances of the Popen class have the following methods:
Check if child process has terminated. Set and return
returncode attribute. Otherwise, returns None.
Wait for child process to terminate. Set and return
returncode attribute.
If the process does not terminate after timeout seconds, raise a
TimeoutExpired exception. It is safe to catch this exception and
retry the wait.
備註
This will deadlock when using stdout=PIPE or stderr=PIPE
and the child process generates enough output to a pipe such that
it blocks waiting for the OS pipe buffer to accept more data.
Use Popen.communicate() when using pipes to avoid that.
備註
When the timeout parameter is not None, then (on POSIX) the
function is implemented using a busy loop (non-blocking call and short
sleeps). Use the asyncio module for an asynchronous wait: see
asyncio.create_subprocess_exec.
在 3.3 版的變更: 新增 timeout。
Interact with process: Send data to stdin. Read data from stdout and stderr,
until end-of-file is reached. Wait for process to terminate and set the
returncode attribute. The optional input argument should be
data to be sent to the child process, or None, if no data should be sent
to the child. If streams were opened in text mode, input must be a string.
Otherwise, it must be bytes.
communicate() returns a tuple (stdout_data, stderr_data).
The data will be strings if streams were opened in text mode; otherwise,
bytes.
Note that if you want to send data to the process's stdin, you need to create
the Popen object with stdin=PIPE. Similarly, to get anything other than
None in the result tuple, you need to give stdout=PIPE and/or
stderr=PIPE too.
If the process does not terminate after timeout seconds, a
TimeoutExpired exception will be raised. Catching this exception and
retrying communication will not lose any output.
The child process is not killed if the timeout expires, so in order to cleanup properly a well-behaved application should kill the child process and finish communication:
proc = subprocess.Popen(...)
try:
outs, errs = proc.communicate(timeout=15)
except TimeoutExpired:
proc.kill()
outs, errs = proc.communicate()
備註
The data read is buffered in memory, so do not use this method if the data size is large or unlimited.
在 3.3 版的變更: 新增 timeout。
Sends the signal signal to the child.
Do nothing if the process completed.
備註
On Windows, SIGTERM is an alias for terminate(). CTRL_C_EVENT and
CTRL_BREAK_EVENT can be sent to processes started with a creationflags
parameter which includes CREATE_NEW_PROCESS_GROUP.
Stop the child. On POSIX OSs the method sends SIGTERM to the
child. On Windows the Win32 API function TerminateProcess() is called
to stop the child.
Kills the child. On POSIX OSs the function sends SIGKILL to the child.
On Windows kill() is an alias for terminate().
The following attributes are also set by the class for you to access. Reassigning them to new values is unsupported:
The args argument as it was passed to Popen -- a
sequence of program arguments or else a single string.
在 3.3 版被加入.
If the stdin argument was PIPE, this attribute is a writeable
stream object as returned by open(). If the encoding or errors
arguments were specified or the text or universal_newlines argument
was True, the stream is a text stream, otherwise it is a byte stream.
If the stdin argument was not PIPE, this attribute is None.
If the stdout argument was PIPE, this attribute is a readable
stream object as returned by open(). Reading from the stream provides
output from the child process. If the encoding or errors arguments were
specified or the text or universal_newlines argument was True, the
stream is a text stream, otherwise it is a byte stream. If the stdout
argument was not PIPE, this attribute is None.
If the stderr argument was PIPE, this attribute is a readable
stream object as returned by open(). Reading from the stream provides
error output from the child process. If the encoding or errors arguments
were specified or the text or universal_newlines argument was True, the
stream is a text stream, otherwise it is a byte stream. If the stderr argument
was not PIPE, this attribute is None.
警告
Use communicate() rather than .stdin.write,
.stdout.read or .stderr.read to avoid
deadlocks due to any of the other OS pipe buffers filling up and blocking the
child process.
The process ID of the child process.
Note that if you set the shell argument to True, this is the process ID
of the spawned shell.
The child return code. Initially None, returncode is set by
a call to the poll(), wait(), or communicate() methods
if they detect that the process has terminated.
A None value indicates that the process hadn't yet terminated at the
time of the last method call.
A negative value -N indicates that the child was terminated by signal
N (POSIX only).
The STARTUPINFO class and following constants are only available
on Windows.
Partial support of the Windows
STARTUPINFO
structure is used for Popen creation. The following attributes can
be set by passing them as keyword-only arguments.
在 3.7 版的變更: Keyword-only argument support was added.
A bit field that determines whether certain STARTUPINFO
attributes are used when the process creates a window.
si = subprocess.STARTUPINFO()
si.dwFlags = subprocess.STARTF_USESTDHANDLES | subprocess.STARTF_USESHOWWINDOW
If dwFlags specifies STARTF_USESTDHANDLES, this attribute
is the standard input handle for the process. If
STARTF_USESTDHANDLES is not specified, the default for standard
input is the keyboard buffer.
If dwFlags specifies STARTF_USESTDHANDLES, this attribute
is the standard output handle for the process. Otherwise, this attribute
is ignored and the default for standard output is the console window's
buffer.
If dwFlags specifies STARTF_USESTDHANDLES, this attribute
is the standard error handle for the process. Otherwise, this attribute is
ignored and the default for standard error is the console window's buffer.
If dwFlags specifies STARTF_USESHOWWINDOW, this attribute
can be any of the values that can be specified in the nCmdShow
parameter for the
ShowWindow
function, except for SW_SHOWDEFAULT. Otherwise, this attribute is
ignored.
SW_HIDE is provided for this attribute. It is used when
Popen is called with shell=True.
A dictionary of additional attributes for process creation as given in
STARTUPINFOEX, see
UpdateProcThreadAttribute.
Supported attributes:
Sequence of handles that will be inherited. close_fds must be true if non-empty.
The handles must be temporarily made inheritable by
os.set_handle_inheritable() when passed to the Popen
constructor, else OSError will be raised with Windows error
ERROR_INVALID_PARAMETER (87).
警告
In a multithreaded process, use caution to avoid leaking handles
that are marked inheritable when combining this feature with
concurrent calls to other process creation functions that inherit
all handles such as os.system(). This also applies to
standard handle redirection, which temporarily creates inheritable
handles.
在 3.7 版被加入.
The subprocess module exposes the following constants.
The standard input device. Initially, this is the console input buffer,
CONIN$.
The standard output device. Initially, this is the active console screen
buffer, CONOUT$.
The standard error device. Initially, this is the active console screen
buffer, CONOUT$.
Hides the window. Another window will be activated.
Specifies that the STARTUPINFO.hStdInput,
STARTUPINFO.hStdOutput, and STARTUPINFO.hStdError attributes
contain additional information.
Specifies that the STARTUPINFO.wShowWindow attribute contains
additional information.
A STARTUPINFO.dwFlags parameter to specify that the
Working in Background mouse cursor will be displayed while a
process is launching. This is the default behavior for GUI
processes.
在 3.13 版被加入.
A STARTUPINFO.dwFlags parameter to specify that the mouse
cursor will not be changed when launching a process.
在 3.13 版被加入.
The new process has a new console, instead of inheriting its parent's console (the default).
A Popen creationflags parameter to specify that a new process
group will be created. This flag is necessary for using os.kill()
on the subprocess.
This flag is ignored if CREATE_NEW_CONSOLE is specified.
A Popen creationflags parameter to specify that a new process
will have an above average priority.
在 3.7 版被加入.
A Popen creationflags parameter to specify that a new process
will have a below average priority.
在 3.7 版被加入.
A Popen creationflags parameter to specify that a new process
will have a high priority.
在 3.7 版被加入.
A Popen creationflags parameter to specify that a new process
will have an idle (lowest) priority.
在 3.7 版被加入.
A Popen creationflags parameter to specify that a new process
will have a normal priority. (default)
在 3.7 版被加入.
A Popen creationflags parameter to specify that a new process
will have realtime priority.
You should almost never use REALTIME_PRIORITY_CLASS, because this interrupts
system threads that manage mouse input, keyboard input, and background disk
flushing. This class can be appropriate for applications that "talk" directly
to hardware or that perform brief tasks that should have limited interruptions.
在 3.7 版被加入.
A Popen creationflags parameter to specify that a new process
will not create a window.
在 3.7 版被加入.
A Popen creationflags parameter to specify that a new process
will not inherit its parent's console.
This value cannot be used with CREATE_NEW_CONSOLE.
在 3.7 版被加入.
A Popen creationflags parameter to specify that a new process
does not inherit the error mode of the calling process. Instead, the new
process gets the default error mode.
This feature is particularly useful for multithreaded shell applications
that run with hard errors disabled.
在 3.7 版被加入.
Prior to Python 3.5, these three functions comprised the high level API to
subprocess. You can now use run() in many cases, but lots of existing code
calls these functions.
Run the command described by args. Wait for command to complete, then
return the returncode attribute.
Code needing to capture stdout or stderr should use run() instead:
run(...).returncode
To suppress stdout or stderr, supply a value of DEVNULL.
The arguments shown above are merely some common ones.
The full function signature is the
same as that of the Popen constructor - this function passes all
supplied arguments other than timeout directly through to that interface.
備註
Do not use stdout=PIPE or stderr=PIPE with this
function. The child process will block if it generates enough
output to a pipe to fill up the OS pipe buffer as the pipes are
not being read from.
在 3.3 版的變更: 新增 timeout。
在 3.12 版的變更: Changed Windows shell search order for shell=True. The current
directory and %PATH% are replaced with %COMSPEC% and
%SystemRoot%\System32\cmd.exe. As a result, dropping a
malicious program named cmd.exe into a current directory no
longer works.
Run command with arguments. Wait for command to complete. If the return
code was zero then return, otherwise raise CalledProcessError. The
CalledProcessError object will have the return code in the
returncode attribute.
If check_call() was unable to start the process it will propagate the exception
that was raised.
Code needing to capture stdout or stderr should use run() instead:
run(..., check=True)
To suppress stdout or stderr, supply a value of DEVNULL.
The arguments shown above are merely some common ones.
The full function signature is the
same as that of the Popen constructor - this function passes all
supplied arguments other than timeout directly through to that interface.
備註
Do not use stdout=PIPE or stderr=PIPE with this
function. The child process will block if it generates enough
output to a pipe to fill up the OS pipe buffer as the pipes are
not being read from.
在 3.3 版的變更: 新增 timeout。
在 3.12 版的變更: Changed Windows shell search order for shell=True. The current
directory and %PATH% are replaced with %COMSPEC% and
%SystemRoot%\System32\cmd.exe. As a result, dropping a
malicious program named cmd.exe into a current directory no
longer works.
Run command with arguments and return its output.
If the return code was non-zero it raises a CalledProcessError. The
CalledProcessError object will have the return code in the
returncode attribute and any output in the
output attribute.
這等同於：
run(..., check=True, stdout=PIPE).stdout
The arguments shown above are merely some common ones.
The full function signature is largely the same as that of run() -
most arguments are passed directly through to that interface.
One API deviation from run() behavior exists: passing input=None
will behave the same as input=b'' (or input='', depending on other
arguments) rather than using the parent's standard input file handle.
By default, this function will return the data as encoded bytes. The actual encoding of the output data may depend on the command being invoked, so the decoding to text will often need to be handled at the application level.
This behaviour may be overridden by setting text, encoding, errors,
or universal_newlines to True as described in
Frequently Used Arguments and run().
To also capture standard error in the result, use
stderr=subprocess.STDOUT:
>>> subprocess.check_output(
... "ls non_existent_file; exit 0",
... stderr=subprocess.STDOUT,
... shell=True)
'ls: non_existent_file: No such file or directory\n'
在 3.1 版被加入.
在 3.3 版的變更: 新增 timeout。
在 3.4 版的變更: 新增 input 關鍵字引數的支援。
在 3.6 版的變更: 新增 encoding 與 errors。細節請見 run()。
在 3.7 版被加入: text was added as a more readable alias for universal_newlines.
在 3.12 版的變更: Changed Windows shell search order for shell=True. The current
directory and %PATH% are replaced with %COMSPEC% and
%SystemRoot%\System32\cmd.exe. As a result, dropping a
malicious program named cmd.exe into a current directory no
longer works.
subprocess Module¶In this section, "a becomes b" means that b can be used as a replacement for a.
備註
All "a" functions in this section fail (more or less) silently if the
executed program cannot be found; the "b" replacements raise OSError
instead.
In addition, the replacements using check_output() will fail with a
CalledProcessError if the requested operation produces a non-zero
return code. The output is still available as the
output attribute of the raised exception.
In the following examples, we assume that the relevant functions have already
been imported from the subprocess module.
output=$(mycmd myarg)
變成：
output = check_output(["mycmd", "myarg"])
output=$(dmesg | grep hda)
變成：
p1 = Popen(["dmesg"], stdout=PIPE)
p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
p1.stdout.close() # Allow p1 to receive a SIGPIPE if p2 exits.
output = p2.communicate()[0]
The p1.stdout.close() call after starting the p2 is important in order for
p1 to receive a SIGPIPE if p2 exits before p1.
Alternatively, for trusted input, the shell's own pipeline support may still be used directly:
output=$(dmesg | grep hda)
變成：
output = check_output("dmesg | grep hda", shell=True)
os.system()¶sts = os.system("mycmd" + " myarg")
# 變成
retcode = call("mycmd" + " myarg", shell=True)
註解：
Calling the program through the shell is usually not required.
The call() return value is encoded differently to that of
os.system().
The os.system() function ignores SIGINT and SIGQUIT signals while
the command is running, but the caller must do this separately when
using the subprocess module.
A more realistic example would look like this:
try:
retcode = call("mycmd" + " myarg", shell=True)
if retcode < 0:
print("Child was terminated by signal", -retcode, file=sys.stderr)
else:
print("Child returned", retcode, file=sys.stderr)
except OSError as e:
print("Execution failed:", e, file=sys.stderr)
os.spawn family¶P_NOWAIT 範例：
pid = os.spawnlp(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg")
==>
pid = Popen(["/bin/mycmd", "myarg"]).pid
P_WAIT 範例：
retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg")
==>
retcode = call(["/bin/mycmd", "myarg"])
Vector example:
os.spawnvp(os.P_NOWAIT, path, args)
==>
Popen([path] + args[1:])
Environment example:
os.spawnlpe(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg", env)
==>
Popen(["/bin/mycmd", "myarg"], env={"PATH": "/usr/bin"})
os.popen(), os.popen2(), os.popen3()¶(child_stdin, child_stdout) = os.popen2(cmd, mode, bufsize)
==>
p = Popen(cmd, shell=True, bufsize=bufsize,
stdin=PIPE, stdout=PIPE, close_fds=True)
(child_stdin, child_stdout) = (p.stdin, p.stdout)
(child_stdin,
child_stdout,
child_stderr) = os.popen3(cmd, mode, bufsize)
==>
p = Popen(cmd, shell=True, bufsize=bufsize,
stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True)
(child_stdin,
child_stdout,
child_stderr) = (p.stdin, p.stdout, p.stderr)
(child_stdin, child_stdout_and_stderr) = os.popen4(cmd, mode, bufsize)
==>
p = Popen(cmd, shell=True, bufsize=bufsize,
stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True)
(child_stdin, child_stdout_and_stderr) = (p.stdin, p.stdout)
Return code handling translates as follows:
pipe = os.popen(cmd, 'w')
...
rc = pipe.close()
if rc is not None and rc >> 8:
print("There were some errors")
==>
process = Popen(cmd, stdin=PIPE)
...
process.stdin.close()
if process.wait() != 0:
print("There were some errors")
popen2 module¶備註
If the cmd argument to popen2 functions is a string, the command is executed through /bin/sh. If it is a list, the command is directly executed.
(child_stdout, child_stdin) = popen2.popen2("somestring", bufsize, mode)
==>
p = Popen("somestring", shell=True, bufsize=bufsize,
stdin=PIPE, stdout=PIPE, close_fds=True)
(child_stdout, child_stdin) = (p.stdout, p.stdin)
(child_stdout, child_stdin) = popen2.popen2(["mycmd", "myarg"], bufsize, mode)
==>
p = Popen(["mycmd", "myarg"], bufsize=bufsize,
stdin=PIPE, stdout=PIPE, close_fds=True)
(child_stdout, child_stdin) = (p.stdout, p.stdin)
popen2.Popen3 and popen2.Popen4 basically work as
subprocess.Popen, except that:
Popen raises an exception if the execution fails.
The capturestderr argument is replaced with the stderr argument.
stdin=PIPE and stdout=PIPE must be specified.
popen2 closes all file descriptors by default, but you have to specify
close_fds=True with Popen to guarantee this behavior on
all platforms or past Python versions.
This module also provides the following legacy functions from the 2.x
commands module. These operations implicitly invoke the system shell and
none of the guarantees described above regarding security and exception
handling consistency are valid for these functions.
Return (exitcode, output) of executing cmd in a shell.
Execute the string cmd in a shell with Popen.check_output() and
return a 2-tuple (exitcode, output).
encoding and errors are used to decode output;
see the notes on Frequently Used Arguments for more details.
A trailing newline is stripped from the output. The exit code for the command can be interpreted as the return code of subprocess. Example:
>>> subprocess.getstatusoutput('ls /bin/ls')
(0, '/bin/ls')
>>> subprocess.getstatusoutput('cat /bin/junk')
(1, 'cat: /bin/junk: No such file or directory')
>>> subprocess.getstatusoutput('/bin/junk')
(127, 'sh: /bin/junk: not found')
>>> subprocess.getstatusoutput('/bin/kill $$')
(-15, '')
適用: Unix, Windows.
在 3.3.4 版的變更: 新增對 Windows 的支援。
The function now returns (exitcode, output) instead of (status, output)
as it did in Python 3.3.3 and earlier. exitcode has the same value as
returncode.
在 3.11 版的變更: 新增 encoding 與 errors 參數。
Return output (stdout and stderr) of executing cmd in a shell.
Like getstatusoutput(), except the exit code is ignored and the return
value is a string containing the command's output. Example:
>>> subprocess.getoutput('ls /bin/ls')
'/bin/ls'
適用: Unix, Windows.
在 3.3.4 版的變更: 新增對 Windows 的支援
在 3.11 版的變更: 新增 encoding 與 errors 參數。
When using the timeout parameter in functions like run(),
Popen.wait(), or Popen.communicate(),
users should be aware of the following behaviors:
Process Creation Delay: The initial process creation itself cannot be interrupted on many platform APIs. This means that even when specifying a timeout, you are not guaranteed to see a timeout exception until at least after however long process creation takes.
Extremely Small Timeout Values: Setting very small timeout values (such as a few
milliseconds) may result in almost immediate TimeoutExpired exceptions because
process creation and system scheduling inherently require time.
On Windows, an args sequence is converted to a string that can be parsed using the following rules (which correspond to the rules used by the MS C runtime):
Arguments are delimited by white space, which is either a space or a tab.
A string surrounded by double quotation marks is interpreted as a single argument, regardless of white space contained within. A quoted string can be embedded in an argument.
A double quotation mark preceded by a backslash is interpreted as a literal double quotation mark.
Backslashes are interpreted literally, unless they immediately precede a double quotation mark.
If backslashes immediately precede a double quotation mark, every pair of backslashes is interpreted as a literal backslash. If the number of backslashes is odd, the last backslash escapes the next double quotation mark as described in rule 3.
也參考
shlexModule which provides function to parse and escape command lines.
vfork() 或 posix_spawn()¶在 Linux 上，subprocess 在安全的情況下預設會在內部使用 vfork() 系統呼叫，而不是 fork()，這顯著地提高了性能。
如果你遇到了一個推定為極異常的情況，需要防止 Python 使用 vfork()，你可以將 subprocess._USE_VFORK 屬性設為 false 值。
subprocess._USE_VFORK = False # 見 CPython 問題 gh-NNNNNN.
設定它並不會影響 posix_spawn() 的使用，它可以在其 libc 實作內部使用 vfork()。如果你需要封鎖該屬性的使用，則有一個類似的 subprocess._USE_POSIX_SPAWN 屬性。
subprocess._USE_POSIX_SPAWN = False # 見 CPython 問題 gh-NNNNNN.
在任何 Python 版本上將這些設定為 false 都是安全的。當不受支援時，它們對舊版本沒有影響。不要假設屬性可供讀取。儘管有它們的名稱，真實值並不表示將使用相應的函式，而只是表示可能會使用。
每當你需要使用這些私有開關以重現你所看到的問題時，請隨時提出問題 (file issues)。從程式碼中的註解連結到該問題。
在 3.8 版被加入: _USE_POSIX_SPAWN
在 3.11 版被加入: _USE_VFORK