Running arbitrary Python code from Python and preserving return values

Question

I am attempting to write an API in Python that will allow me to run arbitrary Python code. In particular, I would like to be able to call any function through the API and have the return value passed back to me. The use case is that I have a Python library from which I would like to call functions from Java. Jython only supports Python 2 and I would prefer not embed Python in C/C++ embedded in Java.

My first instinct is to use exec(), but exec() does not support returning values. E.g, exec('10+20') returns None. Is there a more elegant way to do this than writing the output to a variable within the exec() call? e.g. exec('a=10+20')

compile() in eval mode maybe?

JonSG
– JonSG

2023-03-17 21:34:00 +00:00
Commented Mar 17, 2023 at 21:34 — JonSG
– JonSG, Commented Mar 17, 2023 at 21:34

Brian Zhu · Accepted Answer · 2023-03-21 15:24:26Z

0

My current solution is below, and it even seems to work, which is nice.

import ast

def execute_with_return(code: str):
    tree = ast.parse(code)
    return_expr = None
    if type(tree.body[-1]) == ast.Expr:
        return_expr = tree.body[-1]
        tree.body = tree.body[:-1]
    exec(ast.unparse(tree))
    if return_expr:
        return eval(ast.unparse(return_expr))

edited Mar 21, 2023 at 15:24

answered Mar 21, 2023 at 15:24

Brian Zhu

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