files = ["1.cad","2.bat","1.aa","1.bat"]
a = [i for i in files if i.index(".") == 0 and i.count(".") == 1]
files = sorted([i for i in files if i not in a], key = lambda x: x[x.rindex("."):])
print((a + files))

with open('test11.txt', 'r') as file:
    file = file.read().split('\n')
    file = ''.join(list(map(lambda line: "'" + line + "',\n", file)))
    
with open('newfile.txt', 'w') as f:
    f.write(file)

with open('test11.txt', 'r') as file:
    file = file.read().split('\n')
    file = ''.join(list(map(lambda line: "'" + line + "',\n", file)))
    
with open('newfile.txt', 'w') as f:
    f.write(file)