Complementing a Strand of DNA

We firstly need to reverse the string which we can do by list slicing. We then loop through the now inversed string changing A to T, C to G, etc. We store these values in a list called string_list and join them together (strings are immutable and wanted to avoid repeatedly creating new strings).

def reverse_complement(dna_string: str) -> str:
    """
    Parameters
    ----------
    dna_string : Str
    DNA Nucleotide String (DNA String)   
    
    Returns 
    -------
    Reverse complement of string
    Type: Str
    
    Example
    -------
    Input: AAAACCCGGT
    Output: ACCGGGTTTT
    """
    string_list = []
    dna_string_reverse = dna_string[::-1]
    for nucleotide in dna_string_reverse:
        if nucleotide == 'A':
            string_list.append('T')
        if nucleotide == 'T':
            string_list.append('A')
        if nucleotide == 'C':
            string_list.append('G')
        if nucleotide == 'G':
            string_list.append('C')
               
    return ''.join(string_list)

print(reverse_complement('AAAACCCGGT'))

## ACCGGGTTTT

We could include the slicing in the for loop like below to save memory/time:

for nucleotide in dna_string[::-1]:
    stuff

Complementing a Strand of DNA

Kyle Reese

Senior Data Scientist