Check for blank line after a class definition

shopify_python/google_styleguide.py

@@ -87,6 +87,9 @@ class GoogleStyleGuideChecker(checkers.BaseChecker):
                   'lambda-func',
                   "For common operations like multiplication, use the functions from the operator module"
                   "instead of lambda functions. For example, prefer operator.mul to lambda x, y: x * y."),
+        'C6015': ('No blank line after a class definition',
+                  'blank-line-after-class-required',
+                  'Missing a blank line after a class definition'),
     }
 
     options = (
@@ -173,6 +176,9 @@ def visit_raise(self, node):  # type: (astroid.Raise) -> None
     def visit_if(self, node):
         self.__use_cond_expr(node)  # type: (astroid.If) -> None
 
+    def visit_classdef(self, node):  # type: (astroid.ClassDef) -> None
+        self.__class_def_check(node)
+
     @staticmethod
     def __get_module_names(node):  # type: (astroid.ImportFrom) -> typing.Generator[str, None, None]
         for name in node.names:
@@ -322,3 +328,17 @@ def __lambda_func(self, node):  # type: (astroid.Lambda) -> None
                     lambda_fun = "lambda " + left + ', ' + right + ": " + " ".join([left, node.ops[0][0], right])
                     op_fun = "operator." + operator
                     self.add_message('lambda-func', node=node, args={'op': op_fun, 'lambda_fun': lambda_fun})
+
+    def __class_def_check(self, node):  # type: (astroid.ClassDef) -> None
+        """Enforce a blank line after a class definition line."""
+        prev_line = node.lineno
+
+        for element in node.body:
+            curr_line = element.lineno
+            blank_lines = curr_line - prev_line - 1
+            if isinstance(element, astroid.FunctionDef) and blank_lines < 1:
+                self.add_message('blank-line-after-class-required', node=node)
+                break
+            elif isinstance(element, astroid.FunctionDef):
+                break
+            prev_line = curr_line

tests/functional/blank_line_after_class_required.py

@@ -0,0 +1,4 @@
+# pylint:disable=missing-docstring,invalid-name,too-few-public-methods
+class SomeClass(object):  # [blank-line-after-class-required]
+    def apply(self):
+        pass

tests/functional/blank_line_after_class_required.txt

@@ -0,0 +1 @@
+blank-line-after-class-required:2:SomeClass:No blank line after a class definition

tests/shopify_python/test_google_styleguide.py

@@ -332,3 +332,49 @@ def binaryfnc():
         """.format(expression))
         with self.assertNoMessages():
             self.walk(binary_root)
+
+    def test_class_def_blank_line(self):
+        root = astroid.builder.parse("""
+            class SomePipeline(object):
+                def apply(content):
+                    return content.withColumn('zero', F.lit(0.0))
+
+            class Fact(object):
+                INPUTS = {}
+                def apply(self):
+                    pass
+
+            class Stage(object):
+                INPUTS = {}
+
+                OUTPUTS = {}
+                def apply(self):
+                    pass
+            """)
+        with self.assertAddsMessages(
+            *[pylint.testutils.Message('blank-line-after-class-required', node=root.body[0]),
+              pylint.testutils.Message('blank-line-after-class-required', node=root.body[1]),
+              pylint.testutils.Message('blank-line-after-class-required', node=root.body[2])]
+        ):
+            self.walk(root)
+
+        with self.assertNoMessages():
+            self.walk(astroid.builder.parse("""
+            class SomePipeline(object):
+
+                def apply(content):
+                    return content.withColumn('zero', F.lit(0.0))
+
+            class FirstStage(object):
+                pass
+
+            class SecondStage(object):
+                INPUTS = {}
+                OUTPUTS = {}
+
+                def check():
+                    pass
+
+                def apply():
+                    pass
+            """))