import random
#genF = open ("GenFIle.txt", "w" )
GenList=[]
GenString=''
for i in range(1000):
    NextLetter=random.choice(['A', 'G', 'C', 'T'])
    GenList.append(NextLetter)
GenString=''.join(GenList)
print(GenString)
#myF.write("Моя умная мысль…" )
#GenF.close()