Why does the type error appear if the column is clear?

Question

I checked w_table.iloc[i,4] and didn't find NoneType objects in it. What's the matter could it be?

check = ['word']
for i in range(len(w_table)):
    if w_table.iloc[i, 4] != 'Null':
        if w_table.iloc[i, 4] in check:
            w_table = w_table.drop(w_table.index[i])
        else:
            check = check.append(w_table.iloc[i, 4])
        w_table.index = np.arange(len(w_table))

After executing above code I am getting following TypeError

 TypeError                                 Traceback (most recent call
 last) <ipython-input-74-40b9156195fa> in <module>()

       2 for i in range(len(w_table)):
       3     if w_table.iloc[i, 4] != 'Null':
       4         if w_table.iloc[i, 4] in check:
       5             w_table = w_table.drop(w_table.index[i])
       6         else:

 TypeError: argument of type 'NoneType' is not iterable

Welcome to StackOverflow. Please take the time to read this post on [how to provide a great pandas example](http://stackoverflow.com/questions/20109391/how-to-make-good-reproducible-pandas-examples) as well as how to provide a [minimal, complete, and verifiable example](http://stackoverflow.com/help/mcve) and revise your question accordingly. These tips on [how to ask a good question](http://stackoverflow.com/help/how-to-ask) may also be useful. — jezrael, Jul 23 '18 at 11:31
But it seems problem is with `NaN`s, missing values in column. — jezrael, Jul 23 '18 at 11:32
Can you provide an example of what `w_table` looks like and describe what your trying to do? Generally looping through a DataFrame isn't the best idea and there could be an easier solution here. — vielkind, Jul 23 '18 at 11:32
@vealkind there are some copies of the raws in table and I need to delete them — losya, Jul 23 '18 at 11:35
'check' is None. When using operator `in`, python will look for an iterable. So 'if (...) in check' yields this error if 'check is None'... — rafaelc, Jul 23 '18 at 12:15

jpp · Accepted Answer · 2018-07-23T11:42:31.490

The problem is with this line:

check = check.append(w_table.iloc[i, 4])

list.append is an in-place operation and returns None. Instead, just use:

check.append(w_table.iloc[i, 4])

For better performance, use set and set.add:

check = {'word'}
...
check.add(w_table.iloc[i, 4])

Even better, you can use vectorised functionality to avoid loops altogether. For this, you should provide a complete example, probably in a separate question.

Why does the type error appear if the column is clear?

1 Answers1