subprocessPIPE

subprocess.PIPE is a sentinel value in the Python standard library's subprocess module used to request the creation of a new pipe to a child process. It connects the parent process to one or more of the child’s standard streams (stdin, stdout, and stderr) so that input can be supplied or output captured programmatically. The constant is defined in the module as -1 and is portable across platforms, including Windows and Unix-like systems.

Common usage involves passing PIPE as the value for one or more of the stream parameters when creating a subprocess. For example, one can set stdout=subprocess.PIPE and/or stderr=subprocess.PIPE to capture the child process’s output, or set stdin=subprocess.PIPE to supply input to the child. This mechanism is used with functions such as Popen and run, allowing the parent to interact with the child’s streams either directly or via convenience methods.

A typical pattern is to start a process and read its output using the communicate method, which reads the streams until the process terminates. For instance, running a command and capturing its output can be done with Popen(['cmd', 'args'], stdout=subprocess.PIPE, stderr=subprocess.PIPE) followed by out, err = proc.communicate(). Alternatively, subprocess.run can be used with stdout=subprocess.PIPE and stderr=subprocess.PIPE, or with capture_output=True in newer versions.

Common caveats include the potential for deadlocks if a subprocess produces more data than can be consumed promptly. To avoid this, it is recommended to read from or pipe the process’s output promptly or use the communicate method. PIPE is intended for inter-process communication within a single program and is not the same as shell piping.