import numpy as np
type(np.nan) # float

import numpy as np
print(np.nan + 1) # nan 
print(np.nan - 1) # nan 
print(np.nan * 1) # nan 
print(np.nan / 1) # nan 

import numpy as np
np.nan == np.nan # False
 
bool(np.nan) # True
 
# 輸出結(jié)果:na is not null
if np.nan:
    print('np.nan is not null')  

import numpy as np
np.nan is np.nan # True
np.isnan(np.nan) # True
np.nan in [np.nan] # True

import numpy as np
import pandas as pd
pd.isnull(np.nan)  # True
pd.isna(np.nan)  # True

# None是Python的特殊類型
# NoneType對(duì)象，它只有一個(gè)值None
type(None) # NoneType
None == None # True
None == np.nan # False
 
# 空字符串''
type('') # str

import pandas as pd
import numpy as np
pd.isnull(np.nan) # True
pd.isnull(None) # True
pd.isnull('') # False
pd.isnull('np.nan') # False
pd.isnull('None') # False

import pandas as pd
import numpy as np
List = ['nan', '', 'None', None, np.nan]
for i in List:
    if i == '' or pd.isnull(i) or pd.isnull(float('nan')) or i == 'None':
        print(i)
 
# 上述輸出結(jié)果:
# nan
# ''
# None
# None
# nan