import re

x = [['AATG', 'ATAT', 'GGCC'],
     ['CCTA', 'TCGT', 'AAAA'],
     ['TTAA', 'GGAT', 'TACA']]

pattern = re.compile('[AT]{4}')

y = []
for i in range(len(x[0])):
    y.append(len([j[i] for j in x if pattern.match(j[i])])/len(x))
print(y)