Python: Filtering lists with lambda

Question

Write a Python lambda function which takes a list called my_list and returns a list which includes only even numbers in the same order.

My solution:

f = list(filter(lambda x: (x % 2 == 0), my_list))
print(f)

I'm having issues because I'm doing a homework problem online and it runs various test cases on it and it says my_list isn't defined. Which I understand why that is, because it isn't... but it seems like the question is looking for a broad function which I don't know how to do in this case.

2 questions:

Does my solution look correct?
If so, how do I tailor this so that the homework will accept various inputs?

You can just assign to my_list a list of arbitrary integers as test data, e.g. my_list = [3, 7, 4, 1, 2] — blhsing
– blhsing, Commented Apr 3, 2020 at 17:34
From the first line of your post, maybe you are looking for something like this? f = lambda lst: [x for x in lst if x % 2 == 0] You can call it on any list of integers. — Sufian Latif
– Sufian Latif, Commented Apr 3, 2020 at 17:39

norok2 · Accepted Answer · 2020-04-03 17:38:01Z

1

It does not look correct since f is not a lambda function but a list. OK, it uses lambda but it is not lambda.

You would probably need to write something like:

f = lambda my_list: list(filter(lambda x: (x % 2 == 0), my_list))

or similar.

For example:

f = lambda my_list: [x for x in my_list if x % 2 == 0]

should also satisfy the requirement.

Of course now print(f) will "print the function".

answered Apr 3, 2020 at 17:38

norok2

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desenfirman · Accepted Answer · 2020-04-03 18:11:18Z

1

I'm doing a homework problem online and it runs various test cases

Your function is actually correct. But, well, online coding assessment usually use a stdin as input. Python use input() method to retrieve string from stdin. So if you want your submission accept various input, you probably need to add this.

my_list = list(map(int, input().split(' ')))

That will split string input by space character ' ' to be a list. Then, all content in list converted to integer by map function. Since the return value of map function is not a list, you need list method to convert map result into list. The new list will be saved to my_list variable.

But, again, it depends on your input specification. If your input specification are eg: "1, 2, 4, 5". use ', ' as split parameter.

edited Apr 3, 2020 at 18:11

answered Apr 3, 2020 at 18:03

desenfirman

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