[Tutor] Using exec with dict

[André Roberge]

First things first: I am writing a program which has, among other 
things, an embedded Python interpreter.  So, before telling me that 
"using exec is unsafe because one could enter <...>", consider that the 
user could just as well enter <...> in the interpreter.

(Having gotten this off my chest :-)

In "Python in a Nutshell", Martelli writes, in at least two places, 
something like
"you should use exec only with specific, explicit dictionaries".

I would like to figure out how to do this [yes, for safety reasons :-), 
and also because I am curious] and, so far, I have been unsuccesful.

I have a "robot" that can do some actions like "move()" and 
"turn_left()".  I can program this robot using python like this:
====
.def move_and_turn():
.    move()
.    turn_left()
.
.def draw_square():
.    for i in range(4):
.        move_and_turn()
.
.draw_square()
========
To execute such a program within my larger program, I use
exec code in globals()

where "code" is the little program above, and it works as expected.  The 
question I have is: how do I do this with an explicit dictionary.  I 
would *guess* that this is somehow equivalent to "how do I create a 
dictionary that has access only to robot instructions [move(), 
turn_left(), etc.] and Python's basic syntax" ... but I don't know how 
to do this.

Any help would be appreciated.

André