get ast from python object in interpreter

Question

I am building an application for which I would like a naive user to define a simple function. I would then like to take this function and convert it into an abstract syntax tree. This should also work during an interactive session (i.e using the interpreter). Here's what I have tried so far in the interpreter:

• dill.source.getsource method
• inspect.getsourcemethod
• accessing the function object's __code__ attribute

The first two methods are problematic since they need for the function object to be written in a physical file somewhere in the system. The third one only gave me a byte code version of the code, not useable in ast.parse method.

I am also open to converting a python object directly to abstract syntax but this seems to go against how ast's are supposed to work.

I really need to be able to get an ast from my python object in a regular (not ipython) interpreter. How can I do this?

EDIT

Heres how my "naive user" would interact with my custom library through the interpreter:

>>> import MyLib
>>> def f(x): return x**2
>>> f = MyLib.FunctionAST(f) #FunctionAST will handld the conversion to abstract syntax

Godless

Do users give you a function object or source code? If it's the former, how do they do this without you being able to access the source? – Cromorne

users write out the function and instantiate a class I am creating by passing in the function object. Please see edit to original question for an example. – Godless

The search term for this is "decompile" - if the function's source code is not available then you must decompile its bytecode. – Spire

Where's decompile? I can't find it anywhere?? Could you give an example? – Godless

ast.dump(ast.parse(inspect.getsource(f))) does work when using ipython. It doesn't work in normal python shell because linecache.cache is empty there. If you expect the user to interact in a shell, doesn't it make more sense to use an interactive one? – Nodal

I'd like to make this as flexible as possible... I prefer not to force the user to use any particular shell, but have this work in any python shell. Is there a clean way to force use of ipython? – Godless

I tried dill.source.getsource in a python shell, and it works as expected: ast.dump(ast.parse(dill.source.getsource(f))). Apparently, inspect.getsource doesn't work for objects which are defined interactively. Reference and python bug – Nodal

dill.source.getsource does not work for me and returns OSError: could not extract source code. Are you sure you're not using ipython? What version of dill are you using? – Godless

I am using python 3.6.8 and dill==0.3.1.1. And, yes I am sure that I am in python shell because I tested it again. Check here. – Nodal

The interpreter destroys the AST as soon as it uses it to generate the bytecode. Your request, as stated, is impossible. – Lombardy

Why not just ask the user to provide a string with the source code, instead of the actual function object? – Boneblack