pandas 添加空列并赋空值

创建测试dataframe：

>>> import pandas as pd
>>> df = pd.DataFrame([{'a':1, 'b':2}, {'a':3, 'b':4}])
>>> df
   a  b
0  1  2    
1  3  4 

添加两个空列

>>> df[['c','d']]=df.apply(lambda x:('',''),axis=1,result_type='expand')
>>> df
   a  b c d
0  1  2    
1  3  4 

当然，一列一列添加也是可以的

>>> df['c'] = ''
>>> df['d'] = ''

但如果这样

>>> df[['c', 'd']] = ''
KeyError: "None of [Index(['c', 'd'], dtype='object')] are in the [columns]"