>>> import string
>>> string.ascii_lowercase
'abcdefghijklmnopqrstuvwxyz'
If you really need a list:
>>> list(string.ascii_lowercase)
['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
And to do it with range
>>> list(map(chr, range(97, 123))) #or list(map(chr, range(ord('a'), ord('z')+1)))
['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
Other helpful string
module features:
>>> help(string) # on Python 3
....
DATA
ascii_letters="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
ascii_lowercase="abcdefghijklmnopqrstuvwxyz"
ascii_uppercase="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
digits="0123456789"
hexdigits="0123456789abcdefABCDEF"
octdigits="01234567"
printable="0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&\"()*+,-./:;<=>?@[\\]^_`{|}~ \t\n\r\x0b\x0c'
punctuation = '!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~'
whitespace=" \t\n\r\x0b\x0c"