CODEWITHSUNDEEP
pythonif-statementmultiple-conditions
Jake Schurch
Jake Schurch

Reputation: 135

Is the if statement condition mutually-exclusive to multiple variables?

Let's say that I have three lists and want to add all elements that are integers to a list named int_list: 

test1 = [1, 2, 3, "b", 6]
test2 = [1, "foo", "bar", 7]
test3 = ["more stuff", 1, 4, 99]
int_list = []

I know that I can do the following code to append all integers to a new list:

for elem1, elem2, elem3 in zip(test1, test2, test3):
    if elem1 is int:
        int_list.append(elem1)
    if elem2 is int:
        int_list.append(elem2)
    if elem3 is int:
        int_list.append(elem3)

Is there anyway that I can merge the if statements into one conditional statement? Or make it less code? Is there a more pythonic way to do this? I tried doing the following code, but it would include elements that were not integers:

for elem1, elem2, elem3 in zip(test1, test2, test3):
        if (elem1 is int, elem2 is int, elem3 is int):
            int_list.append(elem1)
            int_list.append(elem2)
            int_list.append(elem3)

Upvotes: 1

Views: 1257

Answers (2)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476594

There are some problems with your code:

  1. zip constructs tuples of elements as long as all lists have elements, if one of the lists is exhausted, zip stops;
  2. elem1 is int does not do type-checking, it does reference equality checking, you can use isinstance(..) for that; and
  3. as @Jean-FrançoisFabre says, the if (...) will always succeed since you test it with a tuple with one or more elements: regardless of the values of that tuple the truthiness is True.

Why not first join them thogether? You can for instance use a tuple of the lists, like:

for sublist in (test1,test2,test3):
    for x in sublist:
        if isinstance(x,int):
            int_list.append(x)

Or you can use list comprehension:

int_list = [x for sublist in (test1,test2,test3)
              for x in sublist if isinstance(x,int)]

Upvotes: 2

Pierce Darragh
Pierce Darragh

Reputation: 2200

You use zip, but you want itertools.chain(). Additionally you should use isinstance to check class membership.

from itertools import chain

for elem in chain(test1, test2, test3):
    if isinstance(elem, int):
        int_list.append(elem)

Upvotes: 2

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