Patched code sample

import ast

def safe_parse_definitions(code_string):
    """
    Safely extracts function and class definitions from a string of Python
    code without executing it by using an Abstract Syntax Tree (AST).

    This represents the fixed approach, replacing a dangerous `exec()` with
    safe parsing. It avoids the execution of potentially malicious default
    arguments in functions or base class expressions in classes.
    """
    completions = {}
    try:
        # The core of the fix: parse the code into a tree of nodes
        # instead of executing it. This is safe and does not evaluate expressions.
        tree = ast.parse(code_string)

        # Iterate through the top-level nodes in the parsed tree.
        for node in tree.body:
            if isinstance(node, ast.FunctionDef):
                # Safely extract the function's name.
                func_name = node.name
                # Safely extract argument names.
                arg_names = [arg.arg for arg in node.args.args]
                # For a completion dictionary, we store a representation.
                # Importantly, default values (node.args.defaults) are NOT
                # evaluated, preventing arbitrary code execution.
                completions[func_name] = f"def {func_name}({', '.join(arg_names)})"

            elif isinstance(node, ast.ClassDef):
                # Safely extract the class's name.
                class_name = node.name
                # Base classes (node.bases) are also part of the AST but are not
                # evaluated here, preventing execution of code in base class lists.
                completions[class_name] = f"class {class_name}"

    except SyntaxError:
        # If the code is not valid Python, parsing fails gracefully
        # without any security risk.
        return {}

    return completions