Question

I’d like to read an object method’s local value from a decorator that wraps it.
I’ve got access to the function and func_code from within the decorator but it seems all I can get out of it is the names of the local vars, but not their values.

Is it possible?

Answer 1

See https://stackoverflow.com/a/4249347/224295, http://code.activestate.com/recipes/577283-decorator-to-expose-local-variables-of-a-function-/

Working example:

import sys

class persistent_locals(object):
    def __init__(self, func):
        self._locals = {}
        self.func = func

    def __call__(self, *args, **kwargs):
        def tracer(frame, event, arg):
            if event=='return':
                self._locals = frame.f_locals.copy()

        # tracer is activated on next call, return or exception
        sys.setprofile(tracer)
        try:
            # trace the function call
            res = self.func(*args, **kwargs)
        finally:
            # disable tracer and replace with old one
            sys.setprofile(None)
        return res

    def clear_locals(self):
        self._locals = {}

    @property
    def locals(self):
        return self._locals

@persistent_locals
def func():
    local1 = 1
    local2 = 2

func()
print func.locals