Pexpected

Pexpected is a Python library designed to automate interactions with command-line applications. It is based on the original Expect utility, which was developed in the 1990s for automating interactive Unix programs. Pexpected allows a Python script to spawn a child program, control its input and output, and respond to expected patterns in the program's output. This is particularly useful for tasks that require user interaction, such as logging into remote servers via SSH, configuring network devices, or running scripts that prompt for user input.

The core functionality of Pexpected revolves around its ability to "expect" certain output strings from the child process and then "send" appropriate responses. This creates a conversational loop between the Python script and the application it is controlling. For example, a script could use Pexpected to log into an SSH server by expecting the "password:" prompt and then sending the user's password. Pexpected supports various matching mechanisms, including literal strings, regular expressions, and timeouts. If a pattern is not matched within a specified timeout, Pexpected can raise an exception, allowing the script to handle unexpected output or program behavior.

Pexpected simplifies complex automation tasks that would otherwise require manual intervention or more intricate scripting. It provides a high-level interface for controlling processes, making it a valuable tool for system administrators, developers, and anyone needing to automate command-line workflows. The library is actively maintained and offers features such as handling different character encodings and supporting asynchronous operations.