replace rows in a pandas data frame
If you are replacing the entire row then you can just use an index and not need row,column slices.
...
data.loc[2]=5,6
I want to start with an empty data frame and then add to it one row each time. 
I can even start with a 0 data frame data=pd.DataFrame(np.zeros(shape=(10,2)),column=["a","b"]) and then replace one line each time. 
How can I do that?