regular expressions an text string

[ragia]

hi
i have to match text string char by char to a regular expressions  tht
just allow digits 0-9 if other thing a ppear it shall be replaced with
space.how can i do that any help?
so far i have the string and can read it using a for loop...but how to
match each char with the regular expressions and save the result into
other string or replace it with space in that other string to have new
one..
I a new in python  ,thatnks in advance