subprocess — Gerenciamento de subprocessos

Código-fonte: Lib/subprocess.py


O módulo subprocess permite que você crie novos processos, conecte-se aos seus canais de entrada/saída/erro e obtenha seus códigos de retorno. Este módulo pretende substituir vários módulos e funções mais antigos:

os.system
os.spawn*

Informações sobre como o módulo subprocess pode ser usado para substituir esses módulos e funções podem ser encontradas nas seções a seguir.

Ver também

PEP 324 – PEP propondo o módulo subprocess

Usando o módulo subprocess

A abordagem recomendada para invocar subprocessos é usar a função run() para todos os casos de uso que ela pode manipular. Para casos de uso mais avançados, a interface subjacente Popen pode ser usada diretamente.

A função run() foi adicionada no Python 3.5; se você precisa manter a compatibilidade com versões anteriores, veja a seção API de alto nível mais antiga.

subprocess.run(args, *, stdin=None, input=None, stdout=None, stderr=None, capture_output=False, shell=False, cwd=None, timeout=None, check=False, encoding=None, errors=None, text=None, env=None, universal_newlines=None, **other_popen_kwargs)

Executa o comando descrito por args. Aguarda a conclusão do comando e retorna uma instância de CompletedProcess.

Os argumentos mostrados acima são meramente os mais comuns, descritos abaixo em Argumentos usados frequentemente (daí o uso de notação somente-nomeado na assinatura abreviada). A assinatura da função completa é basicamente a mesma do construtor Popen - a maioria dos argumentos para esta função são passados para aquela interface. (timeout, input, check e capture_output não são.)

If capture_output is true, stdout and stderr will be captured. When used, the internal Popen object is automatically created with stdout=PIPE and stderr=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, use stdout=PIPE and stderr=STDOUT instead of capture_output.

The timeout argument is passed 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 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=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.

Exemplos:

>>> subprocess.run(["ls", "-l"])  # doesn't capture output
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'')

Novo na versão 3.5.

Alterado na versão 3.6: Adicionado os parâmetros encoding e errors.

Alterado na versão 3.7: Added the text parameter, as a more understandable alias of universal_newlines. Added the capture_output parameter.

class subprocess.CompletedProcess

The return value from run(), representing a process that has finished.

args

Os argumentos usados para iniciar o processo. Pode ser uma lista ou uma string.

returncode

Status de saída do processo filho. Normalmente, um status de saída 0 indica que foi executado com êxito.

Um valor negativo -N indica que o filho foi terminado pelo sinal N (POSIX apenas).

stdout

Stdout capturado do processo filho. Uma sequência de bytes ou uma string se run() foi chamada com uma codificação, erros ou text=True. None se stdout não foi capturado.

Se você executou o processo com stderr=subprocess.STDOUT, stdout e stderr serão combinados neste atributo, e stderr será None.

stderr

Stderr capturado do processo filho. Uma sequência de bytes ou uma string se run() foi chamada com uma codificação, erros ou text=True. None se stderr não foi capturado.

check_returncode()

Se returncode é diferente de zero, levantar um CalledProcessError.

Novo na versão 3.5.

subprocess.DEVNULL

Valor especial que pode ser usado como o argumento stdin, stdout ou stderr para Popen e indica que o arquivo especial os.devnull será usado.

Novo na versão 3.3.

subprocess.PIPE

Valor especial que pode ser usado como o argumento stdin, stdout ou stderr para Popen e indica que um encadeamento para o fluxo padrão deve ser aberto. Mais útil com Popen.communicate().

subprocess.STDOUT

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.

exception subprocess.SubprocessError

Classe base para todas as outras exceções deste módulo.

Novo na versão 3.3.

exception subprocess.TimeoutExpired

Subclasse de SubprocessError, levantada quando um tempo limite expira enquanto espera por um processo filho.

cmd

Command that was used to spawn the child process.

timeout

Tempo limite em segundos.

output

Saída do processo filho se ele foi capturado por run() ou check_output(). Caso contrário, None.

stdout

Alias for output, for symmetry with stderr.

stderr

Saída Stderr do processo filho se ele foi capturado por run(). Caso contrário, None.

Novo na versão 3.3.

Alterado na versão 3.5: Atributos stdout e stderr adicionados

exception subprocess.CalledProcessError

Subclasse de SubprocessError, levantada quando um processo executado por check_call() ou check_output() retorna um status de saída diferente de zero.

returncode

Exit status of the child process. If the process exited due to a signal, this will be the negative signal number.

cmd

Command that was used to spawn the child process.

output

Saída do processo filho se ele foi capturado por run() ou check_output(). Caso contrário, None.

stdout

Alias for output, for symmetry with stderr.

stderr

Saída Stderr do processo filho se ele foi capturado por run(). Caso contrário, None.

Alterado na versão 3.5: Atributos stdout e stderr adicionados

Argumentos usados frequentemente

Para suportar uma ampla variedade de casos de uso, o construtor Popen (e as funções de conveniência) aceita muitos argumentos opcionais. Para a maioria dos casos de uso típicos, muitos desses argumentos podem ser seguramente deixados em seus valores padrão. Os argumentos mais comumente necessários são:

args é necessário para todas as chamadas e deve ser uma string ou uma sequência de argumentos do programa. Fornecer uma sequência de argumentos geralmente é preferível, pois permite que o módulo cuide de qualquer escapamento e citação de argumentos que forem necessários (por exemplo, para permitir espaços em nomes de arquivo). Se for passada uma única string, shell deve ser True (veja abaixo) ou então a string deve apenas nomear o programa a ser executado sem especificar nenhum argumento.

stdin, stdout and stderr specify the executed program’s standard input, standard output and standard error file handles, respectively. Valid values are PIPE, DEVNULL, an existing file descriptor (a positive integer), an existing file object, and None. PIPE indicates that a new pipe to the child should be created. DEVNULL indicates that the special file os.devnull will be used. With the default settings of None, no redirection will occur; the child’s file handles will be inherited from the parent. Additionally, stderr can be STDOUT, 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 separator os.linesep. For stdout and stderr, all line endings in the output will be converted to '\n'. For more information see the documentation of the io.TextIOWrapper class when the newline argument to its constructor is None.

If text mode is not used, stdin, stdout and stderr will be opened as binary streams. No encoding or line ending conversion is performed.

Novo na versão 3.6: Adicionado os parâmetros encoding e errors.

Novo na versão 3.7: Adicionado o parâmetro text como um atalho para universal_newlines.

Nota

The newlines attribute of the file objects Popen.stdin, Popen.stdout and Popen.stderr are not updated by the Popen.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(), and shutil).

Alterado na versão 3.3: When universal_newlines is True, the class uses the encoding locale.getpreferredencoding(False) instead of locale.getpreferredencoding(). See the io.TextIOWrapper class for more information on this change.

Nota

Leia a seção Security Considerations antes de usar shell=True.

Essas opções, junto com todas as outras opções, são descritas em mais detalhes na documentação do construtor Popen.

Construtor Popen

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.

class subprocess.Popen(args, bufsize=-1, executable=None, stdin=None, stdout=None, stderr=None, preexec_fn=None, close_fds=True, shell=False, cwd=None, env=None, universal_newlines=None, startupinfo=None, creationflags=0, restore_signals=True, start_new_session=False, pass_fds=(), *, group=None, extra_groups=None, user=None, umask=-1, encoding=None, errors=None, text=None)

Execute a child program in a new process. On POSIX, the class uses os.execvp()-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.

An example of passing some arguments to an external program as a sequence is:

Popen(["/usr/bin/git", "commit", "-m", "Fixes a bug."])

No POSIX, se args for uma string, a string é interpretada como o nome ou caminho do programa a ser executado. No entanto, isso só pode ser feito se não forem passados argumentos para o programa.

Nota

Pode não ser óbvio como quebrar um comando shell em uma sequência de argumentos, especialmente em casos complexos. shlex.split() pode ilustrar como determinar a tokenização correta para 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) # Success!

Observe em particular que as opções (como -input) e argumentos (como eggs.txt) que são separados por espaços em branco no shell vão em elementos de lista separados, enquanto os argumentos que precisam de aspas ou escape de contrabarra quando usados no shell (como nomes de arquivos contendo espaços ou o comando echo mostrado acima) são um único elemento de lista.

No Windows, se args for uma sequência, será convertido em uma string da maneira descrita em Converter uma sequência de argumentos em uma string no Windows. Isso ocorre porque o CreateProcess() subjacente opera em strings.

Alterado na versão 3.6: O parâmetro args aceita um path-like object se shell é False e uma sequência contendo objetos caminho ou similar no POSIX.

Alterado na versão 3.8: 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.

Nota

Leia a seção Security Considerations antes de usar 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 universal_newlines=True i.e., in a text mode)

  • 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.

Alterado na versão 3.3.1: 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.

Alterado na versão 3.6: executable parameter accepts a path-like object on POSIX.

Alterado na versão 3.8: executable parameter accepts a bytes and path-like object on Windows.

stdin, stdout and stderr specify the executed program’s standard input, standard output and standard error file handles, respectively. Valid values are PIPE, DEVNULL, an existing file descriptor (a positive integer), an existing file object, and None. PIPE indicates that a new pipe to the child should be created. DEVNULL indicates that the special file os.devnull will be used. With the default settings of None, no redirection will occur; the child’s file handles will be inherited from the parent. 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)

Aviso

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. If you must use it, keep it trivial! Minimize the number of libraries you call into.

Nota

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 parameter can take the place of a previously common use of preexec_fn to call os.setsid() in the child.

Alterado na versão 3.8: 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 Herança de descritores de arquivos.

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.

Alterado na versão 3.2: The default for close_fds was changed from False to what is described above.

Alterado na versão 3.7: 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)

Alterado na versão 3.2: O parâmetro pass_fds foi adicionado.

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. In particular, the function looks for executable (or for the first item in args) relative to cwd if the executable path is a relative path.

Alterado na versão 3.6: cwd parameter accepts a path-like object on POSIX.

Alterado na versão 3.7: cwd parameter accepts a path-like object on Windows.

Alterado na versão 3.8: 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)

Alterado na versão 3.2: restore_signals foi adicionado.

If start_new_session is true the setsid() system call will be made in the child process prior to the execution of the subprocess. (POSIX only)

Alterado na versão 3.2: start_new_session foi adicionado.

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)

Availability: POSIX

Novo na versão 3.9.

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)

Availability: POSIX

Novo na versão 3.9.

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)

Availability: POSIX

Novo na versão 3.9.

If umask is not negative, the umask() system call will be made in the child process prior to the execution of the subprocess.

Availability: POSIX

Novo na versão 3.9.

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.

Nota

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 Argumentos usados frequentemente. The universal_newlines argument is equivalent to text and is provided for backwards compatibility. By default, file objects are opened in binary mode.

Novo na versão 3.6: encoding e errors foram adicionados.

Novo na versão 3.7: text foi adicionado como um atalho mais legível para universal_newlines.

If given, startupinfo will be a STARTUPINFO object, which is passed to the underlying CreateProcess function. creationflags, if given, can be one or more of the following flags:

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.

Alterado na versão 3.2: Adicionado suporte a gerenciador de contexto.

Alterado na versão 3.6: O destruidor Popen agora emite um aviso ResourceWarning se o processo filho ainda estiver em execução.

Alterado na versão 3.8: 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.

Exceções

Exceções levantadas no processo filho, antes que o novo programa comece a ser executado, serão levantadas novamente no pai.

A exceção mais comum levantada é OSError. Isso ocorre, por exemplo, ao tentar executar um arquivo inexistente. Os aplicativos devem se preparar para exceções OSError.

A exceção ValueError será levantada se Popen for chamado com argumentos inválidos.

check_call() e check_output() levantarão CalledProcessError se o processo chamado retornar um código de retorno diferente de zero.

Todas as funções e métodos que aceitam um parâmetro de timeout, como call() e Popen.communicate() levantarão TimeoutExpired se o tempo limite expirar antes de o processo terminar.

Todas as exceções definidas neste módulo herdam de SubprocessError.

Novo na versão 3.3: A classe base SubprocessError foi adicionada.

Considerações de Segurança

Unlike some other popen functions, this implementation will never implicitly 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.

When using shell=True, the shlex.quote() function can be used to properly escape whitespace and shell metacharacters in strings that are going to be used to construct shell commands.

Objetos Popen

Instâncias da classe Popen têm os seguintes métodos:

Popen.poll()

Check if child process has terminated. Set and return returncode attribute. Otherwise, returns None.

Popen.wait(timeout=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.

Nota

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.

Nota

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.

Alterado na versão 3.3: timeout foi adicionado.

Popen.communicate(input=None, timeout=None)

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()

Nota

The data read is buffered in memory, so do not use this method if the data size is large or unlimited.

Alterado na versão 3.3: timeout foi adicionado.

Popen.send_signal(signal)

Envia o sinal signal para o filho.

Não faz nada se o processo for concluído.

Nota

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.

Popen.terminate()

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.

Popen.kill()

Kills the child. On POSIX OSs the function sends SIGKILL to the child. On Windows kill() is an alias for terminate().

Os seguintes atributos também estão disponíveis:

Popen.args

O argumento args conforme foi passado para Popen - uma sequência de argumentos do programa ou então uma única string.

Novo na versão 3.3.

Popen.stdin

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 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.

Popen.stdout

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 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.

Popen.stderr

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 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.

Aviso

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.

Popen.pid

O ID de processo do processo filho.

Observe que se você definir o argumento shell como True, este é o ID do processo do shell gerado.

Popen.returncode

The child return code, set by poll() and wait() (and indirectly by communicate()). A None value indicates that the process hasn’t terminated yet.

Um valor negativo -N indica que o filho foi terminado pelo sinal N (POSIX apenas).

Windows Popen Helpers

The STARTUPINFO class and following constants are only available on Windows.

class subprocess.STARTUPINFO(*, dwFlags=0, hStdInput=None, hStdOutput=None, hStdError=None, wShowWindow=0, lpAttributeList=None)

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.

Alterado na versão 3.7: Keyword-only argument support was added.

dwFlags

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
hStdInput

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.

hStdOutput

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.

hStdError

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.

wShowWindow

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.

lpAttributeList

A dictionary of additional attributes for process creation as given in STARTUPINFOEX, see UpdateProcThreadAttribute.

Atributos suportados:

handle_list

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).

Aviso

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.

Novo na versão 3.7.

Constantes do Windows

The subprocess module exposes the following constants.

subprocess.STD_INPUT_HANDLE

The standard input device. Initially, this is the console input buffer, CONIN$.

subprocess.STD_OUTPUT_HANDLE

The standard output device. Initially, this is the active console screen buffer, CONOUT$.

subprocess.STD_ERROR_HANDLE

The standard error device. Initially, this is the active console screen buffer, CONOUT$.

subprocess.SW_HIDE

Oculta a janela. Outra janela será ativada.

subprocess.STARTF_USESTDHANDLES

Specifies that the STARTUPINFO.hStdInput, STARTUPINFO.hStdOutput, and STARTUPINFO.hStdError attributes contain additional information.

subprocess.STARTF_USESHOWWINDOW

Specifies that the STARTUPINFO.wShowWindow attribute contains additional information.

subprocess.CREATE_NEW_CONSOLE

The new process has a new console, instead of inheriting its parent’s console (the default).

subprocess.CREATE_NEW_PROCESS_GROUP

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.

subprocess.ABOVE_NORMAL_PRIORITY_CLASS

A Popen creationflags parameter to specify that a new process will have an above average priority.

Novo na versão 3.7.

subprocess.BELOW_NORMAL_PRIORITY_CLASS

A Popen creationflags parameter to specify that a new process will have a below average priority.

Novo na versão 3.7.

subprocess.HIGH_PRIORITY_CLASS

A Popen creationflags parameter to specify that a new process will have a high priority.

Novo na versão 3.7.

subprocess.IDLE_PRIORITY_CLASS

A Popen creationflags parameter to specify that a new process will have an idle (lowest) priority.

Novo na versão 3.7.

subprocess.NORMAL_PRIORITY_CLASS

A Popen creationflags parameter to specify that a new process will have an normal priority. (default)

Novo na versão 3.7.

subprocess.REALTIME_PRIORITY_CLASS

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.

Novo na versão 3.7.

subprocess.CREATE_NO_WINDOW

A Popen creationflags parameter to specify that a new process will not create a window.

Novo na versão 3.7.

subprocess.DETACHED_PROCESS

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.

Novo na versão 3.7.

subprocess.CREATE_DEFAULT_ERROR_MODE

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.

Novo na versão 3.7.

subprocess.CREATE_BREAKAWAY_FROM_JOB

A Popen creationflags parameter to specify that a new process is not associated with the job.

Novo na versão 3.7.

API de alto nível mais antiga

Antes do Python 3.5, essas três funções constituíam a API de alto nível para subprocesso. Agora você pode usar run() em muitos casos, mas muitos códigos existentes chamam essas funções.

subprocess.call(args, *, stdin=None, stdout=None, stderr=None, shell=False, cwd=None, timeout=None, **other_popen_kwargs)

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.

Nota

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.

Alterado na versão 3.3: timeout foi adicionado.

subprocess.check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False, cwd=None, timeout=None, **other_popen_kwargs)

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.

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.

Nota

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.

Alterado na versão 3.3: timeout foi adicionado.

subprocess.check_output(args, *, stdin=None, stderr=None, shell=False, cwd=None, encoding=None, errors=None, universal_newlines=None, timeout=None, text=None, **other_popen_kwargs)

Executa o comando com argumentos e retorna sua saída.

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.

Isso equivale a:

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 Argumentos usados frequentemente 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'

Novo na versão 3.1.

Alterado na versão 3.3: timeout foi adicionado.

Alterado na versão 3.4: Support for the input keyword argument was added.

Alterado na versão 3.6: encoding and errors were added. See run() for details.

Novo na versão 3.7: text foi adicionado como um atalho mais legível para universal_newlines.

Replacing Older Functions with the subprocess Module

In this section, “a becomes b” means that b can be used as a replacement for a.

Nota

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.

Replacing /bin/sh shell command substitution

output=$(mycmd myarg)

torna-se:

output = check_output(["mycmd", "myarg"])

Replacing shell pipeline

output=$(dmesg | grep hda)

torna-se:

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)

torna-se:

output=check_output("dmesg | grep hda", shell=True)

Substituindo os.system()

sts = os.system("mycmd" + " myarg")
# becomes
retcode = call("mycmd" + " myarg", shell=True)

Notas:

  • 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.

Um exemplo mais realista ficaria assim:

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)

Replacing the os.spawn family

Exemplo P_NOWAIT:

pid = os.spawnlp(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg")
==>
pid = Popen(["/bin/mycmd", "myarg"]).pid

Exemplo P_WAIT:

retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg")
==>
retcode = call(["/bin/mycmd", "myarg"])

Exemplo de vetor:

os.spawnvp(os.P_NOWAIT, path, args)
==>
Popen([path] + args[1:])

Exemplo de ambiente:

os.spawnlpe(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg", env)
==>
Popen(["/bin/mycmd", "myarg"], env={"PATH": "/usr/bin"})

Replacing 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")

Replacing functions from the popen2 module

Nota

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.

Legacy Shell Invocation Functions

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.

subprocess.getstatusoutput(cmd)

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). The locale encoding is used; see the notes on Argumentos usados frequentemente 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, '')

Disponibilidade: POSIX e Windows.

Alterado na versão 3.3.4: Suporte ao Windows foi adicionado.

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.

subprocess.getoutput(cmd)

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'

Disponibilidade: POSIX e Windows.

Alterado na versão 3.3.4: Suporte para Windows adicionado.

Notas

Converter uma sequência de argumentos em uma string no Windows

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):

  1. Arguments are delimited by white space, which is either a space or a tab.

  2. 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.

  3. A double quotation mark preceded by a backslash is interpreted as a literal double quotation mark.

  4. Backslashes are interpreted literally, unless they immediately precede a double quotation mark.

  5. 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.

Ver também

shlex

Module which provides function to parse and escape command lines.