all iteration in list code example

Example 1: list iteration

>>> list('ATGC')
['A', 'T', 'G', 'C']

Example 2: list iteration

def count_v1(dna, base):
    dna = list(dna)  # convert string to list of letters
    i = 0            # counter
    for c in dna:
        if c == base:
            i += 1
    return i