The Magic class's from_file() method begins with an elegant way of catching certain errors. Lines 110-113 in __init__.py:

    def from_file(self, filename):
        # raise FileNotFoundException or IOError if the file does not exist
        with _real_open(filename):
            pass

_real_open() is just Python's builtin open() function. Lines 28-29 in __init__.py:

# avoid shadowing the real open with the version from compat.py
_real_open = open

This causes a problem in an admittedly obscure situation: where the target file is a pipe file (mime type "inode/fifo"). The open() function opens the pipe for reading, and then sits there forever waiting for input that never comes. Which means from_file() also just sits there forever, never calling libmagic.magic_file() or returning any value or throwing any error.

(This is my first time reporting an issue on GitHub. Apologies if I've failed to follow the proper procedure!)