Add feature to get the signature representation of a Python function argument

src/jcloud_docsgen/exceptions.py

@@ -60,4 +60,20 @@ class PythonAnnotationError(ValueError):
         else:
             return f'{self.args[0]}{": " if self.annotation and self.args[0] else ""}{self.annotation if self.args[0] else ""}'
 
-class InvalidPythonAnnotationError(PythonAnnotationError): ...
+class InvalidPythonAnnotationError(PythonAnnotationError): ...
+
+class PythonDefinitionError(ValueError):
+    '''
+    Base class for Python definition errors.
+    '''
+    def __init__(self, *args: object, definition: str = '') -> None:
+        super().__init__(*args)
+        self.definition = definition
+
+    def __str__(self):
+        if not self.args:
+            return ''
+        else:
+            return f'{self.args[0]}{": " if self.definition and self.args[0] else ""}{self.definition if self.args[0] else ""}'
+
+class PythonArgumentStructureError(PythonDefinitionError): ...