CODEWITHSUNDEEP
pythonpython-2.7
wnnmaw
wnnmaw

Reputation: 5534

What is the Correct Syntax for Connecting Multiple Boolean Checks in Python?

So I'm looking for a shorthand way of doing this:

if a == 5 or a == 6 or a == 7:

And having it be something like this:

if a == (5 or 6 or 7):

Now, I know I could do this:

if a in [5,6,7]:

But I'm looking for something more general that would work when the elements can't be easily put into a list (for instance if they are long variable names or if each element is itself a list)

I'm also aware of the any() function, but that doesn't clean it up much (I still have to have a == for each condition).

Can this be done and what is the correct syntax?

EDIT: I know this can be done simply with a bunch of methods, but I'm asking specifically about chaining comparisons together as shown in the second snipit

Upvotes: 0

Views: 228

Answers (3)

aIKid
aIKid

Reputation: 28292

Generally, you can always use the in operator for this. If you want to find something inside a nested list, you can always use itertools.chain.from_iterable. To be honest, right now i couldn't think a case when we couldn't use lists.

For example:

>>> my_list = [[1,2,3],[4,5,6], 6, 7, 2, 3, 'abc']
>>> n = 5
>>> n in itertools.chain.from_iterable(my_list)
True
>>> 
>>> s = 'a' #You can even find if a char exists in the list
>>> s in itertools.chain.from_iterable(my_list)
True

And the answer for your question, do something like in the second snippet? No.

Upvotes: 1

tback
tback

Reputation: 11561

The pythonic way is

if a in (5, 6, 7):
if a in [5, 6, 7]:

The first is also correct:

if a == 5 or a == 6 or a == 7:

The second statement does not do what you think it does:

bool(6 == (5 or 6 or 7))
Out[1]: False

Upvotes: 0

Robᵩ
Robᵩ

Reputation: 168696

The commonly recommended syntax for this is x in <list>, as you've described.

if a in [5,6,7]:

The cases which you claim aren't appropriate work equally well:

# Long names
if a in [the_first_of_november,
         the_second_sunday_in_the_third_lunar_month,
         tuesday]: 


# Lists:
if myList in [yourList, hisList, herList]:

In my opionion, the clearest use of in involves pre-computing the right-hand list:

if my_answer in list_of_correct_answers:

If you are able to construct the list elsewhere, this is perfectly readable for every case you've mentioned.

Upvotes: 2

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