You can use the string module, with string.ascii_uppercase and string.ascii_lowercase.
If you type:
import string
string.ascii_uppercase
You get:
'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
If you type:
string.ascii_lowercase
You’ll get the same result, but in lowercase.
To solve your problem you can do:
import string
upper_case = list(string.ascii_uppercase)
lower_case = list(string.ascii_lowercase)
upper_case and lower_case will be both lists ranging from a to z.
solved How can I create a list from a to z, and A to Z [duplicate]