对pandas数据判断是否为NaN值的方法详解

def age_map(x):
 if x < 26:
  return 0
 elif x >=26 and x <= 35:
  return 1
 elif x > 35 and x <= 45:
  return 2
 elif pd.isnull(x): #判断是否为NaN值，== 和in 都无法判断
  return 3
 else:
  return 4

pd.isnull(x) 

data['age'] = data['birth_year'].map(age_map)