how to extract source code from code objects ?

["Martin v. Löwis"]

Michele Simionato wrote:
> I was hoping for a more built-in solution, as for instance
> an attribute .co_source in code objects. I guess this would be
> inefficient for memory consumption or for other technical reasons.

Can you please explain why you are hoping for a builtin solution?

> My original problem was to convert back to source an AST object
> generated with the parser module. Since parser.st objects can be converted 
> to code objects, I asked how to extract source code from code objects.
> It seems that there is no simple built-in way of doing that (decompyle
> is a few thousands of lines of not so simple Python code).

Generating source from an AST object is much simpler than generating 
source from byte code. However, I still wonder where the need comes from 
in the first place: If you have just created the AST, you surely still 
have a copy of the source code around.

> I guess the reason why there is no standard way to extract the source
> from AST objects is that their implementation (can) change with new
> version of Python, therefore there would be a maintanance issue
> (as it happens with decompyle). Am I correct ?

No. There is no way to do that because nobody ever wanted to do it (or 
atleast no frequently enough to contribute a solution to the standard 
library). If such a thing would be contributed then you are right: there 
would be a maintenance issue. So any volunteer to contribute that 
feature would also need to volunteer to maintain it.

In Python itself, this entire issue is solved more pragmatically: When 
you need the source (e.g. for a traceback), you look at the line number, 
locate the source file, and print the relevant lines.

Regards,
Martin