def convert_part_to_lowercase(s, from_idx, to_idx) :
length = len(s)
if (from_idx < 0 or to_idx > length) : return s
s = list(s)
for i in range(length) :
if ((i >= from_idx and i <= to_idx) and (ord(s[i]) >= 65 and ord(s[i]) <= 90)):
s[i] = chr(ord(s[i]) + 32)
return "".join(s)
s = "PYTHON PROGRAMMING"
s = convert_part_to_lowercase(s, 3, 7);
print(s)
s = convert_part_to_lowercase(s, 11, 12);
print(s)
'''
run:
PYThon pROGRAMMING
PYThon pROGraMMING
'''