Working with File-like Objects
The first argument passed to a
either be a file name or a file-like object, such as
and mutagen will figure out what to do.
If for some reason the automatic type detection fails, it’s possible to pass them using a named argument which skips the type guessing.
Mutagen expects the file offset to be at 0 for all file objects passed to it.
The file-like object has to implement the following interface (It’s a limited subset of real buffered file objects and StringIO/BytesIO)
class IOInterface(object): """This is the interface mutagen expects from custom file-like objects. For loading read(), tell() and seek() have to be implemented. "name" is optional. For saving/deleting write(), flush() and truncate() have to be implemented in addition. fileno() is optional. """ # For loading def tell(self): """Returns he current offset as int. Always >= 0. Raises IOError in case fetching the position is for some reason not possible. """ raise NotImplementedError def read(self, size=-1): """Returns 'size' amount of bytes or less if there is no more data. If no size is given all data is returned. size can be >= 0. Raises IOError in case reading failed while data was available. """ raise NotImplementedError def seek(self, offset, whence=0): """Move to a new offset either relative or absolute. whence=0 is absolute, whence=1 is relative, whence=2 is relative to the end. Any relative or absolute seek operation which would result in a negative position is undefined and that case can be ignored in the implementation. Any seek operation which moves the position after the stream should succeed. tell() should report that position and read() should return an empty bytes object. Returns Nothing. Raise IOError in case the seek operation asn't possible. """ raise NotImplementedError # For loading, but optional @property def name(self): """Should return text. For example the file name. If not available the attribute can be missing or can return an empty string. Will be used for error messages and type detection. """ raise NotImplementedError # For writing def write(self, data): """Write data to the file. Returns Nothing. Raises IOError """ raise NotImplementedError def truncate(self, size=None): """Truncate to the current position or size if size is given. The current position or given size will never be larger than the file size. This has to flush write buffers in case writing is buffered. Returns Nothing. Raises IOError. """ raise NotImplementedError def flush(self): """Flush the write buffer. Returns Nothing. Raises IOError. """ raise NotImplementedError # For writing, but optional def fileno(self): """Returns the file descriptor (int) or raises IOError if there is none. Will be used for low level operations if available. """ raise NotImplementedError
Gio Example Implementation
The following implements a file-like object using PyGObject and Gio. It depends on the giofile Python library.
import mutagen import giofile from gi.repository import Gio gio_file = Gio.File.new_for_uri( "http://people.xiph.org/~giles/2012/opus/ehren-paper_lights-96.opus") cancellable = Gio.Cancellable.new() with giofile.open(gio_file, "rb", cancellable=cancellable) as gfile: print(mutagen.File(gfile).pprint())
$ python example.py Ogg Opus, 228.11 seconds (audio/ogg) ENCODER=opusenc from opus-tools 0.1.5 artist=Ehren Starks title=Paper Lights album=Lines Build Walls date=2005-09-05 copyright=Copyright 2005 Ehren Starks license=http://creativecommons.org/licenses/by-nc-sa/1.0/ organization=magnatune.com