#this works correctly:
abc=''
for i in range(65,91):
    abc=abc+chr(i)
    print(abc)
"""
outputs:
A
AB
ABC
ABCD
.....
"""
#but this doesn't work correctly on Python 3.4.x and above
# for Python 3.3.x I didn't tested
abc=''
for i in range(945,970):
    abc=abc+chr(i)
    print(abc)
"""
outputs
α
α
α
α
α
α
...
instead of
α
αβ
αβγ
αβγδ
...
"""