Question

The title seems stupid but i don’t know how to express it precisely, sorry.

I have a program that need to eval some user code (through RestrictedPython for security) and I want to put a function into the eval’s globals so that it can print out some debug information to me when eval, for example (simplify):

class UserException(Exception):
    pass


def err(msg):
    # ? how to get the globals variable in eval ?
    A = globals().get('A', 'A not found')
    return UserException("%s and A's value is %r" % (msg, A))

g = {
    'err': err,
    'A': None,
    '__builtins__': {},
}

print eval('A or err("A not true")', g)

this will give the resut:

A not true and A's value is 'A not found'

Using ‘globals()’ here insde ‘err’ is of course wrong. But how can i get the value in ‘g’ inside ‘err’?

Answer 1

Any reference to globals() from inside a function will always give you the globals that were in scope when the function was defined. What you are seeing here is no different than when you import a function from one module into another: the imported function still refers to the globals of the module where it was defined.

The simplest way to get the function to use g as its globals() would be to exec the definition using g as the globals. If you do change the globals for the function then don’t foget you also need to include any other globals that the function uses; in this case UserException.

Alternatively you could make err() inspect the stack frame of its caller and use the caller’s globals. That’s messy, but if it’s for debug information may be acceptable to you.

>>> def err(msg):
    # ? how to get the globals variable in eval ?
    A = sys._getframe(1).f_globals.get('A', 'A not found')
    return UserException("%s and A's value is %r" % (msg, A))

>>> import sys
>>> g = {
    'err': err,
    'A': None,
    '__builtins__': {},
}
>>> print eval('A or err("A not true")', g, g)
A not true and A's value is None
>>>