Add path argument to item.write()

Symmetrical to item.read(), this allows us to update the tags of files that are
not in the library. The motivation was this issue [1].

The commit also includes a nasty hack in the plugin code that prevents breaking
other plugins.

[1]: https://github.com/geigerzaehler/beets-check/issues/1

beets/library.py

@@ -414,17 +414,23 @@ class Item(LibModel):
 
         self.path = read_path
 
-    def write(self):
-        """Write the item's metadata to the associated file.
+    def write(self, path=None):
+        """Write the item's metadata to a media file.
+
+        ``path`` defaults to the item's path property.
 
         Can raise either a `ReadError` or a `WriteError`.
         """
+        if path is None:
+            path = self.path
+        else:
+            path = normpath(path)
         try:
-            f = MediaFile(syspath(self.path))
+            f = MediaFile(syspath(path))
         except (OSError, IOError) as exc:
             raise ReadError(self.path, exc)
 
-        plugins.send('write', item=self)
+        plugins.send('write', item=self, path=path)
 
         for key in ITEM_KEYS_WRITABLE:
             setattr(f, key, self[key])

beets/plugins.py

@@ -17,6 +17,7 @@
 import logging
 import traceback
 from collections import defaultdict
+import inspect
 
 import beets
 
@@ -339,4 +340,8 @@ def send(event, **arguments):
     Returns a list of return values from the handlers.
     """
     log.debug('Sending event: %s' % event)
-    return [handler(**arguments) for handler in event_handlers()[event]]
+    for handler in event_handlers()[event]:
+        # Don't break legacy plugins if we want to pass more arguments
+        argspec = inspect.getargspec(handler).args
+        args = dict((k, v) for k, v in arguments.items() if k in argspec)
+        handler(**args)

beetsplug/convert.py

@@ -174,13 +174,12 @@ def convert_item(dest_dir, keep_new, path_formats):
                 encode(item.path, dest)
 
         # Write tags from the database to the converted file.
-        if not keep_new:
-            item.path = dest
-        item.write()
+        item.write(path=dest)
 
-        # If we're keeping the transcoded file, read it again (after
-        # writing) to get new bitrate, duration, etc.
         if keep_new:
+            # If we're keeping the transcoded file, read it again (after
+            # writing) to get new bitrate, duration, etc.
+            item.path = dest
             item.read()
             item.store()  # Store new path and audio data.