gistfile1.txt

from itertools import product

# Chenage AA number here:
repeat = 7

# pepgen
aas = ('ALA', 'ARG', 'ASN', 'ASP', 'CYS', 'GLN', 'GLU', 'GLY', 
       'HIS', 'ILE', 'LEU', 'LYS', 'MET', 'PHE', 'PRO', 'SER', 
       'THR', 'TRP', 'TYR', 'VAL')

all_pep = product(aas, repeat=repeat)

with open('{0}pept.txt'.format(repeat), 'w') as tp:
    for t in all_pep:
        pep = '{0} N{1} {2} C{3} {4}\n'.format('{', t[0],
                                               " ".join(t[1:-1]),
                                               t[-1], '}')
        tp.write(pep)