Python Regular Expression; replacing a portion of match

Question

How would I limit match/replacement the leading zeros in e004_n07? However, if either term contains all zeros, then I need to retain one zero in the term (see example below

Answer 1

edit: Don't let anybody talk you out of validating the format of the fixed data. If that's what you need, don't settle for something overly simple .

Not very pretty, but in a situation that seems fixed, you can just
set all the permutations, then blindly capture the good parts,
leave out the zero's then substitute it all back.

Find ([a-z])(?:([1-9][0-9][0-9])|0([1-9][0-9])|00([1-9]))(_[a-z])(?:([1-9][0-9])|0([1-9]))

Replace $1$2$3$4$5$6$7

Expanded

 ( [a-z] )                     # (1)
 (?:
      ( [1-9] [0-9] [0-9] )         # (2)
   |  
      0
      ( [1-9] [0-9] )               # (3)
   |  
      00
      ( [1-9] )                     # (4)
 )
 ( _ [a-z] )                   # (5)
 (?:
      ( [1-9] [0-9] )               # (6)
   |  
      0
      ( [1-9] )                     # (7)
 )

Output

 **  Grp 0 -  ( pos 0 , len 8 ) 
e004_n07  
 **  Grp 1 -  ( pos 0 , len 1 ) 
e  
 **  Grp 2 -  NULL 
 **  Grp 3 -  NULL 
 **  Grp 4 -  ( pos 3 , len 1 ) 
4  
 **  Grp 5 -  ( pos 4 , len 2 ) 
_n  
 **  Grp 6 -  NULL 
 **  Grp 7 -  ( pos 7 , len 1 ) 
7