Abstract out the duplicated parts of the diffoscope/comparators/debian_fallback.py class.

diffoscope/comparators/debian_fallback.py

@@ -21,10 +21,7 @@
 from .text import TextFile
 
 
-class DotChangesFile(TextFile):
-    DESCRIPTION = "Debian .changes files"
-    FILE_EXTENSION_SUFFIX = '.changes'
-
+class AbstractDebianFallbackFile(TextFile):
     def compare(self, other, *args, **kwargs):
         difference = super().compare(other, *args, **kwargs)
         if not difference:
@@ -35,29 +32,16 @@ class DotChangesFile(TextFile):
         return difference
 
 
-class DotDscFile(TextFile):
-    DESCRIPTION = "Debian .dsc files"
-    FILE_EXTENSION_SUFFIX = '.dsc'
+class DotChangesFile(AbstractDebianFallbackFile):
+    DESCRIPTION = "Debian .changes files"
+    FILE_EXTENSION_SUFFIX = '.changes'
 
-    def compare(self, other, *args, **kwargs):
-        difference = super().compare(other, *args, **kwargs)
-        if not difference:
-            return None
-        difference.add_comment(
-            'Unable to find the "debian" Python module. Falling back to text comparison.'
-        )
-        return difference
+
+class DotDscFile(AbstractDebianFallbackFile):
+    DESCRIPTION = "Debian source packages (.dsc)"
+    FILE_EXTENSION_SUFFIX = '.dsc'
 
 
-class DotBuildinfoFile(TextFile):
+class DotBuildinfoFile(AbstractDebianFallbackFile):
     DESCRIPTION = "Debian .buildinfo files"
     FILE_EXTENSION_SUFFIX = '.buildinfo'
-
-    def compare(self, other, *args, **kwargs):
-        difference = super().compare(other, *args, **kwargs)
-        if not difference:
-            return None
-        difference.add_comment(
-            'Unable to find the "debian" Python module. Falling back to text comparison.'
-        )
-        return difference