Encoding By Rotating the Characters

from string import ascii_letters, ascii_lowercase, ascii_uppercase

def cipher(s, k): # s => String Containing Stream of Characters; k => Shift Value
    str_encoded = ""

    for i in range(len(s)):
        if s[i] in ascii_letters:
            if s[i] in ascii_lowercase:
                new_ord = ord(s[i]) + k

                if new_ord > 122:
                    new_ord = (96 + (new_ord - 122))

                    while True:
                        if (97 <= new_ord <= 122):
                            break
                        else:
                            new_ord = (96 + (new_ord - 122))

                    str_encoded += chr(new_ord)
                else:
                    str_encoded += chr(new_ord)
            elif s[i] in ascii_uppercase:
                new_ord = ord(s[i]) + k

                if new_ord > 90:
                    new_ord = (64 + (new_ord - 90))

                    while True:
                        if (65 <= new_ord <= 90):
                            break
                        else:
                            new_ord = (64 + (new_ord - 90))

                    str_encoded += chr(new_ord)
                else:
                    str_encoded += chr(new_ord)
        else:
            str_encoded += s[i]

    return str_encoded

val = cipher("www.abc.xy", 87)
print(val)