Counting nucleotides in DNA sequence string
<p>I have written this function which does not function as I would like it. Any ideas please?
I understand the problem is somehow on the char definition...</p>

<pre><code>def count_nucleotides(dna, nucleotide):
    ''' (str, str) -&gt; int

    Return the number of occurrences of nucleotide in the DNA sequence dna.

    &gt;&gt;&gt; count_nucleotides('ATCGGC', 'G')
    2
    &gt;&gt;&gt; count_nucleotides('ATCTA', 'G')
    0
    '''

    num_nucleodites=0

    for char in dna:
        if char is ('A'or'T'or'C'or'G'):
            num_nucleodites=num_nucleodites + 1      
    return num_nucleodites
</code></pre>
