pandas去重、缺失

from numpy import nan
from pandas import DataFrame
flag=[]
k=21
flag.append(k)
print(flag[0])
print(len(flag))
a=nan
if a is nan:
    a='KK'
else:
    a=a+','+'KK'
print(a)
b='bd'
if b=='bd':
    print(b)

df=DataFrame({'A':[1,2,1],'B':[1,6,2]})
print(df['A'].isin([2]) ) 
print(df[df['A'].isin([2])] )
print(df)
df=df.drop_duplicates(subset=['A'],keep='last')
print(df)

#结果：

21
1
KK
bd
0    False
1     True
2    False
Name: A, dtype: bool
   A  B
1  2  6
   A  B
0  1  1
1  2  6
2  1  2
   A  B
1  2  6
2  1  2