mlp/src/events.py

Overview:

This Python script provides a utility function, modify_function, which programmatically alters the behavior of a given function. It uses the ast module (Abstract Syntax Trees) and the inspect module to transform the function’s source code, making it return a predefined string regardless of its original implementation.

modify_function (function):

Description: alters the implementation of a passed-in function such that, regardless of its original code, it now returns a specific string: “Modified return value”. This function demonstrates a technique for code manipulation using Python’s abstract syntax trees, which could be applied in more complex scenarios like code analysis, optimization, or transformation.

Parameters:

• func: the function to be modified. It is expected to be a callable object whose source can be inspected.

Process:

• Source extraction: uses inspect.getsource(func) to obtain the source code of the passed-in function.
• AST parsing: converts the source code into an abstract syntax tree using ast.parse(src), allowing for programmatic inspection and modification of the code structure.
• AST modification: traverses the AST using ast.walk(parsed), looking for a FunctionDef node (the definition of the function). Once found, it modifies this node by replacing its body with a new return statement, ensuring the function will return the string “Modified return value”.
• AST Compilation: the modified AST is compiled back into executable Python code using the compile function.
• Namespace execution: executes the compiled code within a new local namespace (local_namespace dictionary) to avoid polluting the global namespace.
• Function replacement: the original function is replaced with the modified version by returning the new function from the local_namespace dictionary, keyed by the original function’s name.
• Returns: a new function with the same name as func but modified such that its body consists solely of a return statement with the fixed value “Modified return value”.