>import pandas as pd 
>data={'state':[1,1,2,2,1,2,2],'pop':['a','b','c','d','b','c','d']}
>frame=pd.DataFrame(data) 
>frame
	pop	state
0	a	1
1	b	1
2	c	2
3	d	2
4	b	1
5	c	2
6	d	2
>frame.drop_duplicates(subset=['pop','state'])
	pop	state
0	a	1
1	b	1
2	c	2
3	d	2

>data_a={'state':[1,1,2],'pop':['a','b','c']}
>data_b={'state':[1,2,3],'pop':['b','c','d']}
>a=pd.DataFrame(data_a)
>a 
	pop	state
0	a	1
1	b	1
2	c	2
>b=pd.DataFrame(data_b) 
>b
	pop	state
0	b	1
1	c	2
2	d	3
>a = a.append(b)
>a = a.append(b)
>result = a.drop_duplicates(subset=['pop','state'],keep=False)
>result
	pop	state
0	a	1