Python 'BrokenPipeError: [Errno 32] Broken pipe' when piping output to head, grep -q or less (e.g. python script.py | head), or 'Exception ignored ... BrokenPipeError' at exit. How do I handle it correctly?

Cause: when your program writes to a pipe and the reader on the other end exits early (head after N lines, grep -q after the first match, less when you quit), the operating system sends SIGPIPE and further writes fail with EPIPE. Python ignores SIGPIPE by default and turns the failed write into BrokenPipeError: [Errno 32] Broken pipe. You can also see 'Exception ignored in ... BrokenPipeError' at shutdown, because Python flushes stdout again on exit. The same error from a socket (for example in a web server or client) means the other side closed the connection; that's a different situation, usually handled by catching the error and closing the connection. Fix for command-line tools whose output gets piped: 1. Catch BrokenPipeError around your main function, then point stdout at os.devnull before exiting so the final flush doesn't raise again. The Python documentation gives this pattern: in the except BrokenPipeError block, open os.devnull, os.dup2() it onto sys.stdout.fileno(), and sys.exit(1). 2. Flush stdout inside the try block (sys.stdout.flush()) so the error is raised where you can catch it, not during interpreter shutdown. 3. Don't 'fix' it by restoring the default SIGPIPE behaviour (signal.signal(SIGPIPE, SIG_DFL)); the Python docs warn this makes the program exit abruptly whenever any socket connection is interrupted while writing. Fix for subprocess pipelines in your own code: 1. When chaining processes with subprocess.Popen, close the parent's copy of the pipe after handing it to the next process, so the first process gets SIGPIPE/EPIPE when the reader exits, as the subprocess docs show. 2. When writing to a child process's stdin, use communicate() and handle BrokenPipeError if the child may exit early. Verify: python script.py | head -n 1 prints one line and exits with no traceback. Sources: https://docs.python.org/3/library/signal.html#note-on-sigpipe https://man7.org/linux/man-pages/man7/pipe.7.html https://docs.python.org/3/library/subprocess.html