How to compare multiple variables to the same value?

Question

I am using Python and I would like to have an if statement with many variables in it.

Such as:

if A, B, C, and D >= 2:
    print (A, B, C, and D)

I realize that this is not the correct syntax and that is exactly the question I am asking — what is the correct Python syntax for this type of an if statement?

see also http://stackoverflow.com/questions/8641089/python-equivalent-of-linq-all-function — Karl Knechtel, Dec 27 '11 at 06:48

score 52 · Accepted Answer · edited Dec 22 '21 at 10:59

52

You want to test a condition for all the variables:

if all(x >= 2 for x in (A, B, C, D)):
    print(A, B, C, D)

This should be helpful if you're testing a long list of variables with the same condition.

If you needed to check:

if A, B, C, or D >= 2:

Then you want to test a condition for any of the variables:

if any(x >= 2 for x in (A, B, C, D)):
    print(A, B, C, D)

edited Dec 22 '21 at 10:59

Tomerikoo

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answered Dec 27 '11 at 04:16

Limbo Peng

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score 20 · Answer 2 · answered Dec 27 '11 at 04:06

20

Another idea:

if min(A, B, C, D) >= 2:
    print A, B, C, D

answered Dec 27 '11 at 04:06

Fred Larson

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1

It works for this particular case, but in general, you can't compare the same condition for multiple variables at once – Óscar López Dec 27 '11 at 04:22
2

`min` means: find the minimum of all the numbers between the parenthesis. If even the minimum is greater or equal than 2, we can conclude that all of the variables are greater or equal than 2 – Óscar López Dec 27 '11 at 04:30
Oh I get it now! I know what Limbo Peng was saying now! Thanks for the help! – chingchong Dec 27 '11 at 04:32
2

`min(...)` won't shortcircuit whereas `all(...)` does – John La Rooy Dec 27 '11 at 10:52
Not so clear but an awesome idea! Solved my problem. Same can be done with `max`, perhaps some other math methods... ;) – GrayedFox Sep 06 '16 at 12:49
Can you explain what you mean when you say that `all(...)` can short circuit? – bendl May 22 '17 at 17:17
1

@bendl: It stops evaluating as soon as the result is known. – Fred Larson May 22 '17 at 17:19
Is there a situation where that's not preferable? – bendl May 22 '17 at 17:20

score 7 · Answer 3 · answered Dec 27 '11 at 04:15

7

I'd probably write this as

v = A, B, C, D
if all(i >= 2 for i in v):
    print v

answered Dec 27 '11 at 04:15

DSM

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Thanks! To clarify the meaning of what you are telling me... If I had A, B, C, and D. Could I just say v = A, B, C, D (RETURN - can't get the code tag to work) if all(v >= 2): (RETURN) print (v)? – chingchong Dec 27 '11 at 04:30
1

@TerriMoore: No, because that would be asking if the tuple (A, B, C, D) was greater than or equal to 2, not whether all the values are >= 2. For technical reasons that won't actually raise an Exception in python 2, it'll just give unexpected results, but it will raise an error (as it should) in python 3. – DSM Dec 27 '11 at 04:34
I am using python 3. What exactly would the "i in v" thing be looking at? – chingchong Dec 27 '11 at 04:36
@LimboPeng's answer is a little more directly implemented, without the intermediate 'v' variable. – PaulMcG Dec 27 '11 at 04:40
OK so you recommend Limbo's answer over DSM's? – chingchong Dec 27 '11 at 04:41

Óscar López · Answer 4 · 2011-12-27T04:38:49.543

3

How about:

if A >= 2 and B >= 2 and C >= 2 and D >= 2:
    print A, B, C, D

For the general case, there isn't a shorter way for indicating that the same condition must be true for all variables - unless you're willing to put the variables in a list, for that take a look at some of the other answers.

edited Dec 27 '11 at 04:38

answered Dec 27 '11 at 04:01

Óscar López

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Thanks! I have 10 variables is their anything that takes less typing? – chingchong Dec 27 '11 at 04:25
If you need to test the same condition (>= 2) and all the variables are numbers, @Fred Larson's answer is the shortest solution (albeit a bit hard to understand at a glance) – Óscar López Dec 27 '11 at 04:28
If I need to do other conditions would the answer provided by DSM be the best? – chingchong Dec 27 '11 at 04:33
Same thing: it works only if the condition is the same for all variables; otherwise you have to test each variable individually, one by one, as in my answer – Óscar López Dec 27 '11 at 04:36
Ya I want them to all be tested against the same condition individually not as a group but I want to put it all into one if statement. – chingchong Dec 27 '11 at 04:39
What I mean as not as a group is not adding them together or anything. I want the if to be: If and only If ALL the variables are less than or greater than 2 do the following. – chingchong Dec 27 '11 at 04:40
Then I'd go with @Limbo Peng's or DSM's answer – Óscar López Dec 27 '11 at 04:40
Thanks I think I will go with Limbo Peng's. – chingchong Dec 27 '11 at 04:43
I am a little confused on the parenthesis used in his answer though. – chingchong Dec 27 '11 at 04:44

score 3 · Answer 5 · answered Dec 27 '11 at 04:32

3

If you have ten variables that you are treating as a group like this, you probably want to make them elements of a list, or values in a dictionary, or attributes of an object. For example:

my_dict = {'A': 1, 'B': 2, 'C': 3 }

if all(x > 2 for x in my_dict.values()):
    print "They're all more than two!"

answered Dec 27 '11 at 04:32

Ned Batchelder

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No that isn't what I am trying to achieve here. But thanks anyways! – chingchong Dec 27 '11 at 04:34

score 2 · Answer 6 · answered Dec 27 '11 at 04:10

2

Depending on what you are trying to accomplish, passing a list to a function may work.

def foo(lst):
    for i in lst:
        if i < 2:
            return
    print lst

answered Dec 27 '11 at 04:10

Phil

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Oops! I've just posted the same answer as yours. LOL – Limbo Peng Dec 27 '11 at 04:17
If you could explain what this is doing in more detail I would really help me. Thanks! – chingchong Dec 27 '11 at 04:26
You pass the function a list of numbers. For each item in the list, check to see if the item is less than 2 - if the item is less than 2, then the function "returns" (or exits) without printing anything. Continue checking each item in the list. Once each item has been checked, and no item caused the function to return/exit, we know that ALL items are >= 2, so we can print the list. – Phil Dec 27 '11 at 05:03

score 1 · Answer 7 · edited Sep 11 '13 at 17:02

1

Except that she's probably asking for this:

if A >= 2 and B >= 2 and C >= 2 and D >= 2:

edited Sep 11 '13 at 17:02

Brad Larson

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answered Dec 27 '11 at 04:03

Dan

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How to compare multiple variables to the same value?

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