RestrictedPython: Call other functions within user-specified code?

Using Yuri Nudelman's code with the custom _import definition to specify modules to restrict serves as a good base but when calling functions within said user_code naturally due to having to whitelist everything is there any way to permit other user defined functions to be called? Open to other sandboxing solutions although Jupyter didn't seem straight-forward to embed within a web interface.

from RestrictedPython import safe_builtins, compile_restricted
from RestrictedPython.Eval import default_guarded_getitem

def _import(name, globals=None, locals=None, fromlist=(), level=0):
    safe_modules = ["math"]
    if name in safe_modules:
       globals[name] = __import__(name, globals, locals, fromlist, level)
    else:
        raise Exception("Don't you even think about it {0}".format(name))

safe_builtins['__import__'] = _import # Must be a part of builtins

def execute_user_code(user_code, user_func, *args, **kwargs):
    """ Executed user code in restricted env
        Args:
            user_code(str) - String containing the unsafe code
            user_func(str) - Function inside user_code to execute and return value
            *args, **kwargs - arguments passed to the user function
        Return:
            Return value of the user_func
    """

    def _apply(f, *a, **kw):
        return f(*a, **kw)

    try:
        # This is the variables we allow user code to see. @result will contain return value.
        restricted_locals = { 
            "result": None,
            "args": args,
            "kwargs": kwargs,
        }   

        # If you want the user to be able to use some of your functions inside his code,
        # you should add this function to this dictionary.
        # By default many standard actions are disabled. Here I add _apply_ to be able to access
        # args and kwargs and _getitem_ to be able to use arrays. Just think before you add
        # something else. I am not saying you shouldn't do it. You should understand what you
        # are doing thats all.
        restricted_globals = { 
            "__builtins__": safe_builtins,
            "_getitem_": default_guarded_getitem,
            "_apply_": _apply,
        }   

        # Add another line to user code that executes @user_func
        user_code += "\nresult = {0}(*args, **kwargs)".format(user_func)

        # Compile the user code
        byte_code = compile_restricted(user_code, filename="<user_code>", mode="exec")

        # Run it
        exec(byte_code, restricted_globals, restricted_locals)
       # User code has modified result inside restricted_locals. Return it.
        return restricted_locals["result"]

    except SyntaxError as e:
        # Do whaever you want if the user has code that does not compile
        raise
    except Exception as e:
        # The code did something that is not allowed. Add some nasty punishment to the user here.
        raise

i_example = """
import math

def foo():
    return 7

def myceil(x):
    return math.ceil(x)+foo()
"""
print(execute_user_code(i_example, "myceil", 1.5))

Running this returns 'foo' is not defined

from RestrictedPython: Call other functions within user-specified code?