As John's reply shows - there are several ways this can be done. Here is an example using regular expressions.
## ConfigureFields Script
import re
#Configure all fields from input 'in1' to be mapped
#to the corresponding fields on the output 'out1'
out1 += in1
out1.DigitsOnly = unicode
pattern = r'^([a-zA-Z]+)(\d+)$'
## ProcessRecords Script
#Copy all fields from input 'in1' to the corresponding output fields
#in output 'out1'. Copies the values of the fields that have been setup
#in the mapping defined in the ConfigureFields property
out1 += in1
if fields.Data == Null or fields.Data == "":
out1.DigitsOnly = Null
else:
match = re.match(pattern, fields.Data)
if match:
out1.DigitsOnly = match.group(2)
else:
out1.DigitsOnly = Null