Best way to append data frame?

[WuchaDoin]

I read by accident, somewhere online, recently that it is highly unsought to append/insert a data frame either row by row, or cell by cell (for iloc). I cannot recall which one exactly, but to the point; What is the best way to append data into a data frame? Here is the snippit I have. I am doing my best to work with PEP8 style guide while making changes at the same time so feel free to mention discrepancies in the style. I have a total of 12 columns and I feel that appending each line singly is not good to do. It looks too separated (for lack of better words to explain it).

                    # Sets the quantity #
                    InvoiceDataFrame.loc[[len(InvoiceDataFrame) - 1],
                                         InvoiceDataFrame.columns[3]]="1"

                    # Sets the class #
                    InvoiceDataFrame.loc[[len(InvoiceDataFrame) - 1],
                                         InvoiceDataFrame.columns[4]]=ClassIndex[LoadedSales.iloc[inx, 1]]

                    # Sets the Job name #
                    InvoiceDataFrame.loc[[len(InvoiceDataFrame) - 1],
                                         InvoiceDataFrame.columns[5]]=HA

                    # Sets the Terms #
                    InvoiceDataFrame.loc[[len(InvoiceDataFrame) - 1],
                                         InvoiceDataFrame.columns[6]]="Redacted"

Note: With regards to PEP8 Style Guide. I haven't taken time yet to change my variable names to match the style guide.