How to check if an integer or string exists in a list

Question

I want to know how I can check if an integer is in a list. Here is some code I made:

# "1" is a string. 10 is an integer.
my_list = ["1", 10]
if int in my_list:
    print("Integer in the list!")

What is wrong with this code? And how do I make it work?

Brian61354270 · Accepted Answer · 2020-07-01T01:08:21.387

3

As mentioned by Cargcigenicate, both int == "1" and int == 10 are False, so the overall check is False. What you want to do is check whether or not an element in the list is an instance of int, not whether or not they are equal to int.

This can be accomplished a bit more concisely by using the builtin any along with a generator expression:

if any(isinstance(x, int) for x in my_list):
    ...

Note that in general using isinstance should be prefered over type when reasoning about the type of an object since the former takes inheritance into account.

edited Jul 01 '20 at 01:08

answered Jul 01 '20 at 01:07

Brian61354270

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Good calls. A little more complicated, but definately the better option – Carcigenicate Jul 01 '20 at 01:08
I also have one more question, how do I check if an item is not a str? – Macintosh Fan Jul 01 '20 at 01:21
1

@MacintoshFan The same technique applies, just [check whether the elements are not strings](https://stackoverflow.com/a/26535728/11082165). I assume you're familiar with the `not` operator? – Brian61354270 Jul 01 '20 at 01:23

score 1 · Answer 2 · answered Jul 01 '20 at 01:00

1

The problem with this is, int == 10 is false. int is a class, and 10 is an instance of the class. That doesn't mean however that they equate to each other.

You'd need to do some preprocessing first. There's many ways to do this, and it ultimately depends on what your end goal is, but as an example:

my_list = ["1", 10]

# Create a new list that holds the type of each element in my_list
types = [type(x) for x in my_list]

if int in types:  # And check against the types, not the instances themselves
    print("Integer in the list!")

answered Jul 01 '20 at 01:00

Carcigenicate

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Assuming that is the most simple way? – Macintosh Fan Jul 01 '20 at 01:05
1

@MacintoshFan If you really wanted to use `in`, probably. The later ate way would be to use a `for x in my_list:` loop and do something like `if type(x) == int:` inside the loop – Carcigenicate Jul 01 '20 at 01:07

How to check if an integer or string exists in a list

2 Answers2