issue_comments: 1489744942

Agreed, and a reference to a pretty authoritative source: https://github.com/python/cpython/blob/3.11/Modules/_io/bufferedio.c#L915

It's confusing the method has a parameter called filename_or_obj but doesn't actually handle filenames.

One workaround is to use os.read when passed a filename, and .read() when passed a file object. Something similar to: python def get_magic_number(filename_or_obj, count=8): if isinstance(filename_or_obj, (str, os.PathLike)): fd = os.open(filename_or_obj, os.RDONLY) # Append os.O_BINARY on windows magic_number = os.read(fd, count) if len(magic_number) != count: raise TypeError("Error reading magic number") os.close(fd) elif isinstance(filename_or_obj, io.BufferedIOBase): if filename_or_obj.seekable(): pos = filename_or_obj.tell() filename_or_obj.seek(0) magic_number = filename_or_obj.read(count) filename_or_obj.seek(pos) else: raise TypeError("File not seekable.") else: raise TypeError("Cannot read magic number.") return magic_number On my laptop (w/ SSD) using os.read is about 2x faster than using .read()