Python script engine

[A]

Hello,
In my application I  would like to allow users to add/use basic  
python  commands but I do not want users to change my code of 
application directly.


For example my program expects 
telephone. number in  format 
+442076812563
but a user sometimes may want to 
supply
0044  207 681 2563
(please note a blank).
Then the user would need
to use  STRING.JOIN  Python function  to get from the user's input 
(0044  207 681 2563) the string that my program expects 
(+442076812563)

Does anyone have any idea how to do that? 

Thank you for help
Ladislav