Difference between != and IF not in

Question

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!

`letter != punctuation` if `letter` and `punctuation` aren't identical — which is always the case in your code. `letter not in punctuation` if `letter` is not _contained_ in `punctuation`. — L3viathan, Nov 08 '21 at 15:40
Good explanation here: [!= vs not in](https://stackoverflow.com/questions/2209755/python-operation-vs-is-not) — Shaddo, Nov 08 '21 at 15:43
@Shaddo That question is asking about an equality check vs. an identity check. OP's question is asking about an equality check vs. a membership check. — Axe319, Nov 08 '21 at 15:56
Btw, rather than use `alphabet.find`, you should create a dictionary of letters to numbers — OneCricketeer, Nov 08 '21 at 16:01

score 3 · Accepted Answer · edited Nov 08 '21 at 15:59

3

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]

edited Nov 08 '21 at 15:59

OneCricketeer

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answered Nov 08 '21 at 15:48

Alexis Leloup

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score 0 · Answer 2 · edited Nov 08 '21 at 15:58

0

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

there is no difference between them

edited Nov 08 '21 at 15:58

OneCricketeer

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answered Nov 08 '21 at 15:46

sMx_7d

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There is a difference, though. – OneCricketeer Nov 08 '21 at 15:58
@OneCricketeer pls tell me what is it – sMx_7d Nov 08 '21 at 16:59
These may result in the same **answer**, `"a" != "ab"` and `"a" not in "ab"`. But this does not mean they operate _the same way_. Also, question was asking about `not in`, not `if not` – OneCricketeer Nov 08 '21 at 17:01

score 0 · Answer 3 · edited Nov 08 '21 at 16:03

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.

Difference between != and IF not in

3 Answers3