How to encrypt lower case input - python-3.x

Question

I am trying to create a simple encryption scheme. The scheme is working fine when I take input of the plain text in uppercase. But when I take input of the plain text in lowercase, it is not decrypted correctly.
Can anyone help me to find out the solution?
Here is my code:
def generateKey(string, key):
key = list(key)
st = list(string)
if len(string) == len(key):
return(key,st)
else:
x=len(string) -len(key)
if x>0:
for i in range(x):
key.append(key[i % len(key)])
else:
y=len(key)-len(string)
for j in range(y):
st.append("X")
return("" . join(key),"" . join(st))
def cipherText(string, key):
cipher_text = []
for i in range(len(string)):
if string[i]== " ":
x = ord(string[I])
i+=1
cipher_text.append(chr(x))
else:
abc = ord(string[i]) + ord(key[I])
x = (abc + 2) % 26
x += ord('A')
cipher_text.append(chr(x))
ci="" . join(cipher_text)
rev = ""
for i in ci:
rev = i + rev
return(rev)
def originalText(cipher_text, key):
orig_text = []
re_rev= ""
for i in cipher_text:
re_rev = i + re_rev
for i in range(len(re_rev)):
if re_rev[i]== " ":
x = ord(re_rev[I])
i+=1
orig_text.append(chr(x))
else:
abc = ord(re_rev[i]) - ord(key[i]) + 26
x = (abc - 2) % 26
x += ord('A')
orig_text.append(chr(x))
return("" . join(orig_text))
if __name__ == "__main__":
string = input("Enter Plain Text: ")
keyword = input("Enter Keyword: ")
key,stri = generateKey(string, keyword)
cipher_text = cipherText(stri,key)
print("Ciphertext :", cipher_text)
print("Original/Decrypted Text :",
originalText(cipher_text, key))