Removing empty parentheses after class name (#180)

black.py

@@ -743,6 +743,9 @@ def append(self, leaf: Leaf, preformatted: bool = False) -> None:
         if not has_value:
             return
 
+        if token.COLON == leaf.type and self.is_class_parenth_empty:
+            del self.leaves[-2:]
+
         if self.leaves and not preformatted:
             # Note: at this point leaf.prefix should be empty except for
             # imports, for which we only preserve newlines.
@@ -840,6 +843,19 @@ def is_yield(self) -> bool:
             and self.leaves[0].value == "yield"
         )
 
+    @property
+    def is_class_parenth_empty(self) -> bool:
+        """Is this class parentheses blank?"""
+        return (
+            bool(self)
+            and len(self.leaves) == 4
+            and self.is_class
+            and self.leaves[2].type == token.LPAR
+            and self.leaves[2].value == "("
+            and self.leaves[3].type == token.RPAR
+            and self.leaves[3].value == ")"
+        )
+
     def contains_standalone_comments(self, depth_limit: int = sys.maxsize) -> bool:
         """If so, needs to be split before emitting."""
         for leaf in self.leaves:
@@ -1125,6 +1141,7 @@ def line(self, indent: int = 0, type: Type[Line] = Line) -> Iterator[Line]:
 
         If any lines were generated, set up a new current_line.
         """
+
         if not self.current_line:
             if self.current_line.__class__ == type:
                 self.current_line.depth += indent

tests/class_blank_parentheses.py

@@ -0,0 +1,71 @@
+class SimpleClassWithBlankParentheses():
+    pass
+
+
+class ClassWithSpaceParentheses():
+    first_test_data = 90
+    second_test_data = 100
+
+    def test_func(self):
+        return None
+
+
+class ClassWithEmptyFunc(object):
+
+    def func_with_blank_parentheses():
+        return 5
+
+
+def public_func_with_blank_parentheses():
+    return None
+
+
+def class_under_the_func_with_blank_parentheses():
+
+    class InsideFunc():
+        pass
+
+
+class NormalClass():
+
+    def func_for_testing(self, first, second):
+        sum = first + second
+        return sum
+
+
+# output
+
+
+class SimpleClassWithBlankParentheses:
+    pass
+
+
+class ClassWithSpaceParentheses:
+    first_test_data = 90
+    second_test_data = 100
+
+    def test_func(self):
+        return None
+
+
+class ClassWithEmptyFunc(object):
+
+    def func_with_blank_parentheses():
+        return 5
+
+
+def public_func_with_blank_parentheses():
+    return None
+
+
+def class_under_the_func_with_blank_parentheses():
+
+    class InsideFunc:
+        pass
+
+
+class NormalClass:
+
+    def func_for_testing(self, first, second):
+        sum = first + second
+        return sum

tests/test_black.py

@@ -325,6 +325,14 @@ def test_fmtonoff(self) -> None:
         black.assert_equivalent(source, actual)
         black.assert_stable(source, actual, line_length=ll)
 
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_remove_empty_parentheses_after_class(self) -> None:
+        source, expected = read_data("class_blank_parentheses")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, line_length=ll)
+
     def test_report(self) -> None:
         report = black.Report()
         out_lines = []