Evaluate multiple variables in one 'if' statement?

Question

Say I have a bunch of variables that are either True or False. I want to evaluate a set of these variables in one if statement to see if they are all False like so:

if var1, var2, var3, var4 == False:
    # do stuff

Except that doesn't work. I know I can do this:

if var1 == False and var2 == False and var3 == False and var4 == False:
    # do stuff

But that's fairly ugly - especially if these if statements are going to occur a lot in my code. Is there any sort of way I can do this evaluation with a cleaner syntax (like the first example)?

score 34 · Accepted Answer · edited Apr 12 '17 at 07:31

34

You should never test a boolean variable with == True (or == False). Instead, either write:

if not (var1 or var2 or var3 or var4):

or use any (and in related problems its cousin all):

if not any((var1, var2, var3, var4)):

or use Python's transitive comparisons:

if var1 == var2 == var3 == var4 == False:

edited Apr 12 '17 at 07:31

Community

1
1

answered Feb 29 '12 at 18:33

phihag

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`not any(...)` is the Pythonic way to do it for the "all False" case, and `all(...)` is for the "all True" case. – Steven T. Snyder Feb 29 '12 at 18:39
`any((var1, var2, var3, var4))` means all will be evaluated regardless which if you were using expensive functions would be pretty inefficient and rather defeats the purpose of any and short circuiting – Padraic Cunningham Dec 06 '15 at 20:06
@PadraicCunningham `var1`, `var2` etc. are all variables, hence the `var`. If they are function calls, you would of cause use something else. – phihag Dec 06 '15 at 20:25

score 7 · Answer 2 · answered Feb 29 '12 at 18:33

7

How about this:

# if all are False
if not any([var1, var2, var3, var4]):
    # do stuff

or:

# if all are True
if all([var1, var2, var3, var4]):
    # do stuff

These are easy to read, since they are in plain English.

answered Feb 29 '12 at 18:33

Steven T. Snyder

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score 3 · Answer 3 · answered Feb 29 '12 at 18:33

3

if all(not v for v in (var1, var2, var3, var4)):

That's for the "all false" branch. For "all true", just do if all((var2, var2, var3, var4)):.

answered Feb 29 '12 at 18:33

ben w

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all false can be shortened to : `if not any((var1, var2, var3, var4)):` – soulcheck Feb 29 '12 at 18:35
@soulcheck You need to put the arguments into an iterable. `any` takes only one argument. – Steven T. Snyder Feb 29 '12 at 18:37
Not necessary to use `not`, and it can make mistakes easier. – Ethan Furman Feb 29 '12 at 21:49

score 3 · Answer 4 · answered Feb 29 '12 at 18:33

3

You can do:

if var1 and var2 and var3 and var4:
     do stuff

answered Feb 29 '12 at 18:33

soulcheck

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score 1 · Answer 5 · answered Feb 29 '12 at 18:34

What about a custom function?

function ListObjectsEqualTo(myList, toValue):
    for i in myList:
        if i != toValue:
            return False
    return True

Now you can use it

if ListObjectsEqualTo((var1, var2, var3, var4), False):
    # do stuff

score 1 · Answer 6 · answered Feb 29 '12 at 18:34

1

You could do:

if var1 == var2 == var3 == var4 == False:
  do_stuff()

But, if the variables evaluate to true or false, you could also do this:

if var1 and var2 and var3 and var4:
  do_stuff()

Or

if all([var1, var2, var3, var4]):
  do_stuff()

answered Feb 29 '12 at 18:34

mipadi

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score 1 · Answer 7 · answered Feb 29 '12 at 18:35

1

>>> not any([False, False])
True
>>> not any([True, False])
False
>>>

Use the any() keyword.

answered Feb 29 '12 at 18:35

hexparrot

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score 0 · Answer 8 · answered Feb 29 '12 at 18:32

0

You can use if var1 == var2 == var3 == False:

answered Feb 29 '12 at 18:32

jbowes

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Evaluate multiple variables in one 'if' statement?

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