Nan check not recognizing Nan

Question

I am using list comprehension to gather facebook links from a list of urls.

Here is the list:

list1 = ['facebook.com','johnsmithfacebook.com','amazon.com','google.com','stackoverflow.com']

Now I'll do list comprehension to grab the facebook urls, returning np.nan if nothing is found:

facebook = [i for i in list1 if 'facebook' in i] or pd.np.nan

And I'll join the strings if a result exists:

if facebook:
    facebook = ', '.join(facebook)

print(facebook)

'facebook.com, johnsmithfacebook.com'

Great. That works.

But if it there are no facebook urls, and np.nan is returned instead, I run into a problem:

# list
list2 = ['amazon','google']

facebook = [i for i in list2 if 'facebook' in i] or np.nan

if facebook: # nan check
    facebook = ', '.join(facebook) # join if not nan

TypeError                                 Traceback (most recent call last)
<ipython-input-52-1856f748f805> in <module>
      1 if facebook:
----> 2     facebook = ', '.join(facebook)

TypeError: can only join an iterable

The facebook variable is nan , so how did it get past the if facebook: check?

print(facebook)

nan

The error can only join an iterable sounds like I'm trying to join None or Nan from what I've read on google, but I tried to make sure nans didn't get past this point.

Answer 1

The or np.nan isn't needed at all, an empty array isn't truthy so it won't enter the if statement.

facebook = [i for i in list2 if 'facebook' in i]

On top of that, you don't even need the if statement since you'll just get an empty string if you try to join an empty list