"""Transforms a Python source code string to mimic Jupyter notebook's behavior for the last expression.

The function processes the input source code to handle the last expression in a way that mimics
Jupyter's behavior, where the last expression's value is automatically displayed. If the last node
in the parsed AST is an expression, it is extracted and modified to print its value if it is not None.
Otherwise, the original source code is returned unchanged.

Args:
    src (str): The Python source code string to be transformed.

Returns:
    str: The transformed source code string that mimics Jupyter's behavior for the last expression.
"""