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to RNA Transcription in the Python Track

Published at Aug 01 2019 · 0 comments
Test suite


This exercise has changed since this solution was written.

Given a DNA strand, return its RNA complement (per RNA transcription).

Both DNA and RNA strands are a sequence of nucleotides.

The four nucleotides found in DNA are adenine (A), cytosine (C), guanine (G) and thymine (T).

The four nucleotides found in RNA are adenine (A), cytosine (C), guanine (G) and uracil (U).

Given a DNA strand, its transcribed RNA strand is formed by replacing each nucleotide with its complement:

  • G -> C
  • C -> G
  • T -> A
  • A -> U

Exception messages

Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include a message.

To raise a message with an exception, just write it as an argument to the exception type. For example, instead of raise Exception, you should write:

raise Exception("Meaningful message indicating the source of the error")

Running the tests

To run the tests, run the appropriate command below (why they are different):

  • Python 2.7: py.test rna_transcription_test.py
  • Python 3.4+: pytest rna_transcription_test.py

Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version): python -m pytest rna_transcription_test.py

Common pytest options

  • -v : enable verbose output
  • -x : stop running tests on first failure
  • --ff : run failures from previous test before running other test cases

For other options, see python -m pytest -h

Submitting Exercises

Note that, when trying to submit an exercise, make sure the solution is in the $EXERCISM_WORKSPACE/python/rna-transcription directory.

You can find your Exercism workspace by running exercism debug and looking for the line that starts with Workspace.

For more detailed information about running tests, code style and linting, please see Running the Tests.


Hyperphysics http://hyperphysics.phy-astr.gsu.edu/hbase/Organic/transcription.html

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


import unittest

from rna_transcription import to_rna

# Tests adapted from `problem-specifications//canonical-data.json` @ v1.3.0

class RnaTranscriptionTest(unittest.TestCase):

    def test_empty_rna_sequence(self):
        self.assertEqual(to_rna(""), "")

    def test_transcribes_cytosine_to_guanine(self):
        self.assertEqual(to_rna('C'), 'G')

    def test_transcribes_guanine_to_cytosine(self):
        self.assertEqual(to_rna('G'), 'C')

    def test_transcribes_thymine_to_adenine(self):
        self.assertEqual(to_rna('T'), 'A')

    def test_transcribes_adenine_to_uracil(self):
        self.assertEqual(to_rna('A'), 'U')

    def test_transcribes_all_occurrences(self):
        self.assertEqual(to_rna('ACGTGGTCTTAA'), 'UGCACCAGAAUU')

if __name__ == '__main__':
def to_rna(dna_strand):
    nucleotides = {'C': 'G', 'G': 'C', 'T': 'A', 'A': 'U'}
    rna_strand = ''

    for nucleotide in dna_strand:
        rna_strand += nucleotides[nucleotide]

    return rna_strand

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