API design discussion
kk=DataFrame({'a':[1,0,3,5],'b':[2,4,6,8]})
kk['c']=kk.b/kk.a

> > > kk
> > >    a  b  c
> > > 0  1  2  2
> > > 1  0  4  0
> > > 2  3  6  2
> > > 3  5  8  1

Two issues: 
(1) I don't think  kk[1,'c']=0 is a suitable answer
(2) I don't think  kk[3,'c']=1 is a suitable answer, it should be 1.6

while kk['c']=1.0*kk.b/kk.a  give an OK answer

> > > kk
> > >    a  b    c
> > > 0  1  2  2.0
> > > 1  0  4  NaN
> > > 2  3  6  2.0
> > > 3  5  8  1.6

So pls treat 'int/int' to 'float/float', for current 'int/int' treatment will cause difficult checking error
