#! /usr/bin/env python
#import regular expression module
import re

#setting the DNA string
myDNA = 'ACGTTGCAACGTTGCAACGTTGCA'

#assigning a new regex and compiling it 
#to find all Ts
regexp = re.compile('T')

#create a new string tha will
#receive the regex result with
#Us replacing Ts
myRNA = regexp.sub('U', myDNA)

print myRNA