code: def count_nans(df):
      
      cols = df.columns
      res = []
      for col in cols:
          length = len(df[col])
          not_nas = len(df[col].dropna())
          nas = length - not_nas
          rate = round(nas/length, 4)
          # add unique value
          uv = len(df[col].unique())
          res_ = (col, nas, not_nas, rate, uv)
          res.append(res_)
      nas_df = pd.DataFrame(res, columns=['Column', 'NaNs', 'Not_NaNs',
                                          'Rate', 'UV'])
      return nas_df
docs: Count the total number of NaNs in every column
  
      Parameters
      --------------------
          df    pd.DataFrame
  
      Returns
      --------------------
          nas_df    pd.DataFrame