PICARD-1809: Load based on extensions, fallback to guessing if it fails

picard/file.py

@@ -165,7 +165,16 @@ class File(QtCore.QObject, Item):
         if self.tagger.stopping:
             log.debug("File not loaded because %s is stopping: %r", PICARD_APP_NAME, self.filename)
             return None
-        return self._load(filename)
+        try:
+            # Try loading based on extension first
+            return self._load(filename)
+        except Exception:
+            from picard.formats import guess_format
+            # If it fails, force format guessing and try loading again
+            file_format = guess_format(filename)
+            if not file_format and type(file_format) == type(self):
+                raise
+            return file_format._load(filename)
 
     def _load(self, filename):
         """Load metadata from the file."""

picard/formats/__init__.py

@@ -79,15 +79,16 @@ def guess_format(filename, options=_formats):
 def open_(filename):
     """Open the specified file and return a File instance with the appropriate format handler, or None."""
     try:
-        # First try to guess the format on the basis of file headers
-        audio_file = guess_format(filename)
-        if not audio_file:
-            i = filename.rfind(".")
-            if i < 0:
-                return None
+        # Use extension based opening as default
+        i = filename.rfind(".")
+        if i >= 0:
             ext = filename[i+1:].lower()
-            # Switch to extension based opening if guess_format fails
             audio_file = _extensions[ext](filename)
+        else:
+            # If there is no extension, try to guess the format based on file headers
+            audio_file = guess_format(filename)
+        if not audio_file:
+            return None
         return audio_file
     except KeyError:
         # None is returned if both the methods fail