Transcribing DNA into RNA

a="GAGATACCTACGACGGGCGCAGGGACCTGTATTCGAGGCAAGCCAGGCCGCTTTATACCGTCTGCTTCCGCCTCCGGGCCTTCAACTGCATGGTATTAGGTTATGATGCGGAACTAGTTTACTTCGGACGGCCCAGCACTTTGATTATCGTGCCAGATGTAAAGCGATGATCTCCAGGAACCATAAGCAATGAAAATGACCGGATCACCCATTGGCGCCCTGGGTCATCAACAAACCCACAACTCTCCGGTTTGTGACAGACAGTCATGCGGTGGTTCAGATCATCACCACGCGTAGAAATGTAACAGCAGGCAACAGATAATAATAAGTGGCGGGGAATAGTTAATGGGAGAACGTACGGGAACCAGTCCGGAGATATAGTCGTCGCTACCGCAGCTCCCATAGACTCGGTTGGCTTATCTCTAGTGTCCGTCGCCCTTCATGACGTCGGCGTGAAAACCAAGGGTTCAGCTTGTCGGGCGTAGTAAAATTGCCTTACACAGTTGATTCTAAATCCTACCGAAAGTTTGAGGAGAGGAATTGCAATAGGGCGGAGGCCCGGACACACCTCAGGCCAGGTCCATGCACGGCTACATCTCGAAAATCGACGGCACGATCGAGGCGAGAGATGGATATGACCCGTTTTCAGTGCTTTCATCTAGCTATTGGCGCCGCAGAACATTAGCTGGCGTGTACTTCCAGTACGCCCTAATGAACGCACGCTTGTGCTAAGCGGGTCTCTGGAACAGGACCAAGGCAAGCTTTGGGTTGTGTTAGAGCACTTTCAGCACGCGAGCGCAATTGGGACTAGCTGGTAAGAACATTACTAGCGCCAGGATGATCACTACATAAGGCGCATATACACTGTCAGCTCCCCGGGCCTCGCAACGAGGTGCCCTGTGGTTTGAAGGGCAGGACTGCGGGTCCCAAGGCCGTTGTCTGGAAAACCACTTGGCTGG"
a= a.replace("T","U")
print(a)

An RNA string is a string formed from the alphabet containing 'A', 'C', 'G', and 'U'.

Given a DNA string t$t$ corresponding to a coding strand, its transcribed RNA string u$u$ is formed by replacing all occurrences of 'T' in t$t$ with 'U' in u$u$.

Given: A DNA string t$t$ having length at most 1000 nt.

Return: The transcribed RNA string of t$t$.