Python subprocess hangs forever in a non-interactive agent or CI job because the child waits for input (a y/N prompt, a password, a pager). How do I prevent it?

Cause: The child process inherits the parent's stdin by default (the subprocess documentation says stdin=None means no redirection). In an agent, CI runner or background job there is no person to answer, so a confirmation prompt, credential prompt or pager waits indefinitely. Without a timeout the parent waits as well. Fix (best first): 1. Give the child no stdin: subprocess.run(cmd, stdin=subprocess.DEVNULL, capture_output=True, text=True, timeout=300). DEVNULL gives it an empty input, so a prompt reading from stdin gets end-of-file instead of blocking. Alternatively pass input="..." only when you know exactly what the program expects. 2. Always set a timeout. With subprocess.run, on timeout the child is killed and waited for, then TimeoutExpired is raised. With Popen.communicate(timeout=...) the child is not killed; you must call proc.kill() and then communicate() again to drain the pipes. 3. Use the tool's own non-interactive switch instead of piping answers: for example pip has --no-input (environment variable PIP_NO_INPUT); package managers and CLIs usually have a yes or non-interactive flag, so check the tool's help. Choose flags that skip a prompt safely; don't blindly force destructive confirmations. 4. Prevent pagers by passing the tool's no-pager option or setting its pager environment variable (for example for git, git --no-pager); check the tool's docs. 5. Prefer passing credentials via environment variables or credential helpers rather than prompts. 6. When an agent runs commands, tell it to use non-interactive flags and to stop and report if a command asks a question. Don't: use shell=True with unsanitised strings just to pipe a yes into a command, and don't answer every prompt automatically with yes for commands that delete or overwrite data. Verify: run the command in a test with stdin=DEVNULL and a short timeout; it should exit or raise TimeoutExpired rather than hang, and no orphaned process remains. Sources: https://docs.python.org/3/library/subprocess.html https://pip.pypa.io/en/stable/cli/pip/