我认为需要 DataFrame.loc ：

I think to need DataFrame.loc:

A = pd.DataFrame({
    'A': ['a','a','a','a','b','b','b','c','d'],
    'B': list(range(9))
})
print (A)
   A  B
0  a  0
1  a  1
2  a  2
3  a  3
4  b  4
5  b  5
6  b  6
7  c  7

I = [1,3]
B = A.loc[I]
print (B)
   A  B
1  a  1
3  a  3