how to get the amount of nan values in a data fram

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

#where A is the name of the column
#where df is the name of the dataframe
count = df["A"].isna().sum()