SubprocessLauncher

Added in version 2.40.

class SubprocessLauncher(**properties: Any)

Superclasses: Object

This class contains a set of options for launching child processes, such as where its standard input and output will be directed, the argument list, the environment, and more.

While the Subprocess class has high level functions covering popular cases, use of this class allows access to more advanced options. It can also be used to launch multiple subprocesses with a similar configuration.

Constructors

class SubprocessLauncher

classmethod new(flags: SubprocessFlags) → SubprocessLauncher

Creates a new SubprocessLauncher.

The launcher is created with the default options. A copy of the environment of the calling process is made at the time of this call and will be used as the environment that the process is launched in.

Added in version 2.40.

Parameters:

flags – SubprocessFlags

Methods

class SubprocessLauncher

close() → None

Closes all the file descriptors previously passed to the object with take_fd(), take_stderr_fd(), etc.

After calling this method, any subsequent calls to spawn() or spawnv() will return CLOSED. This method is idempotent if called more than once.

This function is called automatically when the SubprocessLauncher is disposed, but is provided separately so that garbage collected language bindings can call it earlier to guarantee when FDs are closed.

Added in version 2.68.

getenv(variable: str) → str | None

Returns the value of the environment variable variable in the environment of processes launched from this launcher.

On UNIX, the returned string can be an arbitrary byte string. On Windows, it will be UTF-8.

Added in version 2.40.

Parameters:

variable – the environment variable to get

set_cwd(cwd: str) → None

Sets the current working directory that processes will be launched with.

By default processes are launched with the current working directory of the launching process at the time of launch.

Added in version 2.40.

Parameters:

cwd – the cwd for launched processes

set_environ(env: Sequence[str]) → None

Replace the entire environment of processes launched from this launcher with the given ‘environ’ variable.

Typically you will build this variable by using listenv() to copy the process ‘environ’ and using the functions environ_setenv(), environ_unsetenv(), etc.

As an alternative, you can use setenv(), unsetenv(), etc.

Pass an empty array to set an empty environment. Pass None to inherit the parent process’ environment. As of GLib 2.54, the parent process’ environment will be copied when set_environ() is called. Previously, it was copied when the subprocess was executed. This means the copied environment may now be modified (using setenv(), etc.) before launching the subprocess.

On UNIX, all strings in this array can be arbitrary byte strings. On Windows, they should be in UTF-8.

Added in version 2.40.

Parameters:

env – the replacement environment

set_flags(flags: SubprocessFlags) → None

Sets the flags on the launcher.

The default flags are NONE.

You may not set flags that specify conflicting options for how to handle a particular stdio stream (eg: specifying both STDIN_PIPE and STDIN_INHERIT).

You may also not set a flag that conflicts with a previous call to a function like set_stdin_file_path() or take_stdout_fd().

Added in version 2.40.

Parameters:

flags – SubprocessFlags

set_stderr_file_path(path: str | None = None) → None

Sets the file path to use as the stderr for spawned processes.

If path is None then any previously given path is unset.

The file will be created or truncated when the process is spawned, as would be the case if using ‘2>’ at the shell.

If you want to send both stdout and stderr to the same file then use STDERR_MERGE.

You may not set a stderr file path if a stderr fd is already set or if the launcher flags contain any flags directing stderr elsewhere.

This feature is only available on UNIX.

Added in version 2.40.

Parameters:

path – a filename or None

set_stdin_file_path(path: str | None = None) → None

Sets the file path to use as the stdin for spawned processes.

If path is None then any previously given path is unset.

The file must exist or spawning the process will fail.

You may not set a stdin file path if a stdin fd is already set or if the launcher flags contain any flags directing stdin elsewhere.

This feature is only available on UNIX.

Added in version 2.40.

Parameters:

path – a filename or None

set_stdout_file_path(path: str | None = None) → None

Sets the file path to use as the stdout for spawned processes.

If path is None then any previously given path is unset.

The file will be created or truncated when the process is spawned, as would be the case if using ‘>’ at the shell.

You may not set a stdout file path if a stdout fd is already set or if the launcher flags contain any flags directing stdout elsewhere.

This feature is only available on UNIX.

Added in version 2.40.

Parameters:

path – a filename or None

setenv(variable: str, value: str, overwrite: bool) → None

Sets the environment variable variable in the environment of processes launched from this launcher.

On UNIX, both the variable’s name and value can be arbitrary byte strings, except that the variable’s name cannot contain ‘=’. On Windows, they should be in UTF-8.

Added in version 2.40.

Parameters:

• variable – the environment variable to set, must not contain ‘=’

• value – the new value for the variable

• overwrite – whether to change the variable if it already exists

spawnv(argv: Sequence[str]) → Subprocess

Creates a Subprocess given a provided array of arguments.

Added in version 2.40.

Parameters:

argv – Command line arguments

take_fd(source_fd: int, target_fd: int) → None

Transfer an arbitrary file descriptor from parent process to the child. This function takes ownership of the source_fd; it will be closed in the parent when self is freed.

By default, all file descriptors from the parent will be closed. This function allows you to create (for example) a custom pipe() or socketpair() before launching the process, and choose the target descriptor in the child.

An example use case is GNUPG, which has a command line argument --passphrase-fd providing a file descriptor number where it expects the passphrase to be written.

Parameters:

• source_fd – File descriptor in parent process

• target_fd – Target descriptor for child process

take_stderr_fd(fd: int) → None

Sets the file descriptor to use as the stderr for spawned processes.

If fd is -1 then any previously given fd is unset.

Note that the default behaviour is to pass stderr through to the stderr of the parent process.

The passed fd belongs to the SubprocessLauncher. It will be automatically closed when the launcher is finalized. The file descriptor will also be closed on the child side when executing the spawned process.

You may not set a stderr fd if a stderr file path is already set or if the launcher flags contain any flags directing stderr elsewhere.

This feature is only available on UNIX.

Added in version 2.40.

Parameters:

fd – a file descriptor, or -1

take_stdin_fd(fd: int) → None

Sets the file descriptor to use as the stdin for spawned processes.

If fd is -1 then any previously given fd is unset.

Note that if your intention is to have the stdin of the calling process inherited by the child then STDIN_INHERIT is a better way to go about doing that.

The passed fd is noted but will not be touched in the current process. It is therefore necessary that it be kept open by the caller until the subprocess is spawned. The file descriptor will also not be explicitly closed on the child side, so it must be marked O_CLOEXEC if that’s what you want.

You may not set a stdin fd if a stdin file path is already set or if the launcher flags contain any flags directing stdin elsewhere.

This feature is only available on UNIX.

Added in version 2.40.

Parameters:

fd – a file descriptor, or -1

take_stdout_fd(fd: int) → None

Sets the file descriptor to use as the stdout for spawned processes.

If fd is -1 then any previously given fd is unset.

Note that the default behaviour is to pass stdout through to the stdout of the parent process.

The passed fd is noted but will not be touched in the current process. It is therefore necessary that it be kept open by the caller until the subprocess is spawned. The file descriptor will also not be explicitly closed on the child side, so it must be marked O_CLOEXEC if that’s what you want.

You may not set a stdout fd if a stdout file path is already set or if the launcher flags contain any flags directing stdout elsewhere.

This feature is only available on UNIX.

Added in version 2.40.

Parameters:

fd – a file descriptor, or -1

unsetenv(variable: str) → None

Removes the environment variable variable from the environment of processes launched from this launcher.

On UNIX, the variable’s name can be an arbitrary byte string not containing ‘=’. On Windows, it should be in UTF-8.

Added in version 2.40.

Parameters:

variable – the environment variable to unset, must not contain ‘=’

Properties

class SubprocessLauncher

props.flags: SubprocessFlags

SubprocessFlags for launched processes.

Added in version 2.40.