try .. except
:
try:
key = int(input('key : '))
# => success
# more code
except ValueError:
print('Enter a number only')
def main():
abc = 'AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz'
message = input("What's the message to encrypt/decrypt? ")
choice = input("Choose: encrypt or decrypt. ")
def readKey():
try:
return int(input("What number would you like for your key value? "))
except ValueError:
return readKey()
key = readKey()
if choice == "encrypt":
encrypt(abc, message, key)
elif choice == "decrypt":
encrypt(abc, message, key * (-1))
else:
print("Bad answer, try again.")
def encrypt(abc, message, key):
text = ""
for letter in message:
if letter in abc:
newPosition = (abc.find(letter) + key * 2) % 52
text += abc[newPosition]
else:
text += letter
print(text)
return text
main()