How to make a continuous alphabetic list python (from a-z then from aa, ab, ac etc)

Use itertools.product.

from string import ascii_lowercase
import itertools

def iter_all_strings():
    for size in itertools.count(1):
        for s in itertools.product(ascii_lowercase, repeat=size):
            yield "".join(s)

for s in iter_all_strings():
    print(s)
    if s == 'bb':
        break

Result:

a
b
c
d
e
...
y
z
aa
ab
ac
...
ay
az
ba
bb

This has the added benefit of going well beyond two-letter combinations. If you need a million strings, it will happily give you three and four and five letter strings.

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Bonus style tip: if you don't like having an explicit break inside the bottom loop, you can use islice to make the loop terminate on its own:

for s in itertools.islice(iter_all_strings(), 54):
    print s

You can use a list comprehension.

from string import ascii_lowercase
L = list(ascii_lowercase) + [letter1+letter2 for letter1 in ascii_lowercase for letter2 in ascii_lowercase]