count nan pandas

#Python, pandas
#Count missing values for each column of the dataframe df

df.isnull().sum()

In [5]: df = pd.DataFrame({'a':[1,2,np.nan], 'b':[np.nan,1,np.nan]})

In [6]: df.isna().sum()
Out[6]:
a    1
b    2
dtype: int64

# Count total missing values in a dataframe

df.isnull().sum().sum()

# Gives a integer value

In [1]: s = pd.Series([1,2,3, np.nan, np.nan])

In [4]: s.isna().sum()   # or s.isnull().sum() for older pandas versions
Out[4]: 2