I am a beginner in Python programming and I have a question about constructing a code.
Let's say I have the following data:
150 z   Brazil
160 a   Toys R Us
I want to code such that if we see the pattern bbb \t (one digit or character not a) \t, I would replace the bbb \t digit \t with bbb_$d$_. (Here, \t indicates tab and bbb indicates a number).
Thus, the output would be 150_$z$_Brazil, and the output for 160 a   Toys R Us would not be obtained as the digit after 160 is a. 
My question is, how do I code such that I select one digit or character that is not a?
 
                        
Q. how do I code such that I select one digit or character that is not a?
A.
'[^a]'The regular expression syntax is documented here.