Append column to pandas dataframe

This is probably easy, but I have the following data:

In data frame 1:

    index dat1
    0     9
    1     5

In data frame 2:

    index dat2
    0     7
    1     6

I want a data frame with the following form:

    index dat1  dat2
    0     9     7
    1     5     6

I've tried using the append method, but I get a cross join (i.e. cartesian product).

What's the right way to do this?

It seems in general you're just looking for a join:

    > dat1 = pd.DataFrame({'dat1': [9,5]})
    > dat2 = pd.DataFrame({'dat2': [7,6]})
    > dat1.join(dat2)
       dat1  dat2
    0     9     7
    1     5     6

From: stackoverflow.com/q/20602947