pandas check if column is null with query function

Question

I have pandas dataframe that I want to execute on it query function with isnull() or not isnull() condition like that:

In [67]: df_data = pd.DataFrame({'a':[1,20,None,40,50]}) In [68]: df_data Out[68]:       a          0   1.0          1  20.0          2   NaN          3  40.0          4  50.0 

if I use this command:

df_data.query('a isnull', engine='python') 

or this command:

df_data.query('a isnull()', engine='python') 

I get an error:

In [75]: df_data.query('a isnull', engine='python')   File "<unknown>", line 1    a isnull            SyntaxError: invalid syntax  In [76]: df_data.query('a isnull()', engine='python')   File "<unknown>", line 1    a isnull ()            SyntaxError: invalid syntax 

What is the right way to do that?

Thank you.

Answer 1

Use .:

a = df_data.query('a.isnull()', engine='python') print (a)     a 2 NaN  b = df_data.query('a.notnull()', engine='python') print (b)       a 0   1.0 1  20.0 3  40.0 4  50.0 

---

You can use also logic NaN != NaN:

a = df_data.query('a != a') print (a)     a  2 NaN  b = df_data.query('a == a') print (b)       a 0   1.0 1  20.0 3  40.0 4  50.0