How to get dynamically-created fxn's source?
gb345 at invalid.com
Fri Nov 5 17:55:31 CET 2010
For a project I'm working on I need a way to retrieve the source
code of dynamically generated Python functions. (These functions
are implemented dynamically in order to simulate "partial application"
in Python.) The ultimate goal is to preserve a textual record
of transformations performed on data, along with all the data (both
pre- and post- transformation) itself.
These transformation functions could be dynamically generated as
closures, but I suspect that this would make it more difficult to
extract source code that could serve as a reasonably self-contained
description of the transformation (because this source code would
refer to variables defined outside of the function). An alternative
would be to generate the *source code* for the functions dynamically,
from a template having slots (within the function's definition)
that gets filled in with actual parameter values, and pass this
source code to exec.
In any case, the problem remains of how to extract the
dynamically-generated function's source code.
One possibility would be to define a Transformation wrapper class
whose __init__ takes the dynamically-generated source code (a
string) as argument, keeps it around as an instance attribute for
future reference, and exec's it to define its __call__ method.
Is this overkill/reinventing the wheel? IOW, does Python already
have a built-in way to achieve this same effect?
(Also, the wrapper scheme above is somewhat loose: it's relatively
easy for the source code instance attribute (as described) to fall
out of sync with the function that actually executes when __call__
runs. Maybe a tighter connection between the obtained source code
and the code that actually executes when __call__ runs is possible.)
I'm aware of the inspect module, but from reading its source code
I gather that it is designed for inspecting source code that is
explicitly written in files, and would not be too good at inspecting
functions that are generated dynamically (i.e. not from source code
explicitly given in a source file--I hope that made sense).
Your comments and suggestions would be much appreciated. Many
thanks in advance!
 For example, given a base function spam that has the signature
(typeT, typeT, typeT, int, int, int) and three specific integer
values X, Y, and Z, dynamically generate a new function spamXYZ
with signature (typeT, typeT, typeT) such that spamXYZ(A, B, C) is
identical to spam(A, B, C, X, Y, Z), for all possible values of A,
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