diff --git a/sphinx/pycode/parser.py b/sphinx/pycode/parser.py
index 9f9f7dd29..f9489e91a 100644
--- a/sphinx/pycode/parser.py
+++ b/sphinx/pycode/parser.py
@@ -383,10 +383,15 @@ class VariableCommentPicker(ast.NodeVisitor):
 
     def visit_AsyncFunctionDef(self, node):
         # type: (ast.AsyncFunctionDef) -> None
+        """Handles AsyncFunctionDef node and set context."""
         self.visit_FunctionDef(node)  # type: ignore
 
 
 class DefinitionFinder(TokenProcessor):
+    """Python source code parser to detect location of functions,
+    classes and methods.
+    """
+
     def __init__(self, lines):
         # type: (List[str]) -> None
         super().__init__(lines)
@@ -397,6 +402,7 @@ class DefinitionFinder(TokenProcessor):
 
     def add_definition(self, name, entry):
         # type: (str, Tuple[str, int, int]) -> None
+        """Add a location of definition."""
         if self.indents and self.indents[-1][0] == 'def' and entry[0] == 'def':
             # ignore definition of inner function
             pass
@@ -405,6 +411,7 @@ class DefinitionFinder(TokenProcessor):
 
     def parse(self):
         # type: () -> None
+        """Parse the code to obtain location of definitions."""
         while True:
             token = self.fetch_token()
             if token is None:
@@ -426,6 +433,7 @@ class DefinitionFinder(TokenProcessor):
 
     def parse_definition(self, typ):
         # type: (str) -> None
+        """Parse AST of definition."""
         name = self.fetch_token()
         self.context.append(name.value)
         funcname = '.'.join(self.context)
@@ -447,6 +455,7 @@ class DefinitionFinder(TokenProcessor):
 
     def finalize_block(self):
         # type: () -> None
+        """Finalize definition block."""
         definition = self.indents.pop()
         if definition[0] != 'other':
             typ, funcname, start_pos = definition