Codon table

Here's a quick code snippet to generate a codon table in Python. The 'table' is actually a dictionary that takes a three-letter, lowercase codon as a key, and returns a single uppercase letter corresponding to the encoded amino acid (or '*' if it's a stop codon).

bases = ['t', 'c', 'a', 'g']
codons = [a+b+c for a in bases for b in bases for c in bases]
codon_table = dict(zip(codons, amino_acids))

So if you type codon_table['atg'], you'll get M for methionine. If you prefer to use 'u' rather than 't', simply change the base in the first line.

It's now quite easy to make a function to translate a gene into an amino acid sequence.

def translate(seq):
    seq = seq.lower().replace('\n', '').replace(' ', '')
    peptide = ''
    for i in xrange(0, len(seq), 3):
        codon = seq[i: i+3]
        amino_acid = codon_table.get(codon, '*')
        if amino_acid != '*':
            peptide += amino_acid
    return peptide

This function takes a DNA sequence, converts it to lowercase and removes any line breaks or spaces. Then it loops through it in chunks of 3, i.e. codons, translating them until it hits a stop codon or a codon not in the dictionary. It returns the amino acid sequence of the resulting peptide.