boolean not in python

Question

I leaned C of the last summer from K&R book from 1989. I am now learning python3.

I am a little confused about something.

In C if i do a test

if !(.....) The '!' changes the value in the '( )' to the opposite, so if it was true, it becomes false and vis versa.

So what i was trying to do, is change this from C to python.

int card(long long number, int size){
    if(!(size == 13 || size == 15 || size == 16)) { // test to see if valid size.
        printf("INVALID\n");
        return 0;
    }

When i tried

def card(number, size):
    if !(size == 13 or size == 15 or size == 16):
        print("INVALID")
        return 0

I got a syntax error.

So after searching on-line I found "is not" in the python3 doc.

so i try it on the interactive terminal.

   >>> if is not (size == 13 or size == 15 or size == 16):
  File "<stdin>", line 1
    if is not (size == 13 or size == 15 or size == 16):
        ^

The interpreter was saying the 'is' is a syntax error. So i decided to remove it and see what happens. And it worked!

I searched on-line and i do not find the 'not' without the 'is'?

Is it OK to use 'if not ( ......)' as the equivalent of 'if !(......)' in C? Or will i get into problems? Or is there a different python way of doing this?

Just simply do if not (...):; In python is is the identity comparison operator (i.e. check whether the value assigned to a given variable is literally the same as the other). — metatoaster
– metatoaster, Commented Apr 24, 2017 at 3:33
Also that is not is also an operator. Related: stackoverflow.com/questions/18275616/… — metatoaster
– metatoaster, Commented Apr 24, 2017 at 3:38

OneCricketeer · Accepted Answer · 2017-04-24 03:52:31Z

1

Is it OK to use 'if not ( ......)' as the equivalent of 'if !(......)' in C?

Sure. Try it.

However, I think you're missing the in keyword.

You can write this

if(!(size == 13 || size == 15 || size == 16)) {

As this

if size not in {13, 15, 16}:

answered Apr 24, 2017 at 3:52

OneCricketeer

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6 Comments

Manny_Mar Over a year ago

Never thought of using a dictionary to do the comparison. In C there is no such class similar to a dictionary. If i used an array, it would only compare the first element, unless i used a "for loop" and index to test each one item, since an array is really just a pointer to the beginning of a continues block of memory, and using it name without an index, get you to index 0. <br/>your example worked fine.<br/> if size not in {13, 15, 16}: <br/>I thought python dictionaries where value pairs such as: dict = {'Name': 'Zara'} Your answer did work, but it's not value pairs, can you explain that?

OneCricketeer Over a year ago

It's not a dictionary, it's a set

OneCricketeer Over a year ago

You can also use a list. if size not in [13, 15, 16]

Manny_Mar Over a year ago

I thought { } meant dictionary. [ ] was a list and ( ) was a tuple

Manny_Mar Over a year ago

Thanks. I have not seen sets yet. I am up to dictionaries in the tutorial i am taking.

|

Community · Accepted Answer · 2017-05-23 12:34:12Z

0

"is" means two variables point the same object,the same Memory address U can see the link Is there a difference between `==` and `is` in Python?

edited May 23, 2017 at 12:34

CommunityBot

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answered Apr 24, 2017 at 3:36

Yang MingHui

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