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

src/jcloud_docsgen/core/python/arguments.py

@@ -17,7 +17,7 @@ from enum import Enum
 from typing import Union
 import ast
 from ...utils import assert_that_is_instance
-from ...exceptions import InvalidPythonIdentifierError, InvalidPythonAnnotationError
+from ...exceptions import InvalidPythonIdentifierError, InvalidPythonAnnotationError, PythonArgumentStructureError
 import keyword
 import types
 
@@ -68,6 +68,9 @@ class PythonFunctionArgument:
         self.kind = kind
         self.default = default
         self.annotation = annotation
+        
+        if self.kind in (PythonArgumentKind.VARARG, PythonArgumentKind.KWARGS) and self.default is not None:
+            raise PythonArgumentStructureError('* or ** arguments cannot have default values', definition = self.signature_repr())
 
     def __eq__(self, value: PythonFunctionArgument) -> bool:
         if not isinstance(value, PythonFunctionArgument):
@@ -82,6 +85,31 @@ class PythonFunctionArgument:
             self.annotation
         ))
 
+    def signature_repr(self) -> str:
+        '''
+        Returns the function signature representation of the argument.
+
+        :return: The string representation of the argument.
+        :rtype: str
+        '''
+
+        if self.kind == PythonArgumentKind.KWARGS:
+            str_repr = '**'
+        elif self.kind == PythonArgumentKind.VARARG:
+            str_repr = '*'
+        else:
+            str_repr = ''
+
+        str_repr += self.name
+
+        if self.annotation is not None:
+            str_repr += ': ' + self.annotation
+
+        if self.default is not None:
+            str_repr += ' = ' + self.default
+
+        return str_repr
+
 class PythonASTArgumentsListParser:
     '''
     A parser for making ``PythonFunctionArgument`` objects from an

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): ...