IMPR: simplify diff.Hunk.create_diff

- remove check_line and replace it with a single f-string
- create a prefix dict for tags and prefixes
- combine processing for equal and delete tags

Change-Id: Ia1e0e1aff06ee440f37ffed92605d62d7e0c60ba

pywikibot/diff.py

@@ -93,25 +93,20 @@ def create_diff(self) -> Iterable[str]:
         Check each line ends with line feed to prevent behaviour like
         :issue:`46395`
         """
-        def check_line(line: str) -> str:
-            r"""Make sure each line ends with '\n'."""
-            return line if line.endswith('\n') else line + '\n'
-
+        lf = '\n'  # required for Python < 3.12
+        prefix = {'insert': '+ ', 'delete': '- ', 'replace': '', 'equal': '  '}
         for tag, i1, i2, j1, j2 in self.group:
             # equal/delete/insert add additional space after the sign as it's
             # what difflib.ndiff does do too.
-            if tag == 'equal':
-                for line in self.a[i1:i2]:
-                    yield '  ' + check_line(line)
-            elif tag == 'delete':
-                for line in self.a[i1:i2]:
-                    yield '- ' + check_line(line)
-            elif tag == 'insert':
+            if tag == 'insert':
                 for line in self.b[j1:j2]:
-                    yield '+ ' + check_line(line)
+                    yield f'{prefix[tag]}{line.strip(lf)}{lf}'
             elif tag == 'replace':
                 for line in difflib.ndiff(self.a[i1:i2], self.b[j1:j2]):
-                    yield check_line(line)
+                    yield f'{prefix[tag]}{line.strip(lf)}{lf}'
+            else:  # equal, delete
+                for line in self.a[i1:i2]:
+                    yield f'{prefix[tag]}{line.strip(lf)}{lf}'
 
     def format_diff(self) -> Iterable[str]:
         """Color diff lines."""