Difference between != and IF not in-CodePudding

can somebody please explain me the difference between if i use "if not ... in" or "!=" in my code

alphabet = "abcdefghijklmnopqrstuvwxyz"
punctuation = ".,?'! "
message = "xuo jxuhu! jxyi yi qd unqcfbu ev q squiqh syfxuh. muhu oek qrbu je tusetu yj? y xefu ie! iudt cu q cuiiqwu rqsa myjx jxu iqcu evviuj!"
translated_message = ""
for letter in message:
    if letter != punctuation:
        letter_value = alphabet.find(letter)
        translated_message  = alphabet[(letter_value   10) % 26]
    else:
        translated_message  = letter
print(translated_message)

output:

heyjtherejjthisjisjanjexamplejofjajcaesarjcipherjjwerejyoujablejtojdecodejitjjijhopejsojjsendjmejajmessagejbackjwithjthejsamejoffsetj

if i use "If not letter in message"

i get this as output:

hey there! this is an example of a caesar cipher. were you able to decode it? i hope so! send me a message back with the same offset!

CodePudding user response：

NOT IN search if the target element is another element : "b" in "abc" should return True

!= or == compares the elements of the two sides of the equality and not their belonging : "b" == "abc" should return False

for letter in message:
    translated_message  = letter if letter in punctuation else alphabet[(alphabet.find(letter)   10) % 26]

CodePudding user response：

The in operator is used to determine whether or not a string is a substring of another string. (Same goes to not in) For example,

if "tom" in "tomato":  
if "cat" in "catalogue":  
if "2" in "234":  
if "4" not in "890":  # or ... if not ("4" in "890")

And so on.
Similarly, != operator is used to compare the values on either sides of them and decide the relation among them. ( a != b ) means If values of two operands are not equal, then condition becomes true. So, it's not good to use this operator to check a particular string is included inside another string.

CodePudding user response：

the != means (Not equal to) and if not means (Not equal to) also!

there is no difference between them