Let's assume you have your dataframe already, we use the Code you provided:
import pandas as pddf = pd.read_csv("sample.csv")Your extra columns should be stored in a list, this makes your Code easier to write and easier to understand.
additional_cols = ['grade','address','attendance','total']The best way to add multiple columns is reindex like U11-Forward suggested.
mydf = df.reindex(df.columns.tolist() + additional_cols, axis = 1)A similar question has been asked here[1]: How to add an empty column to a dataframe?
Regarding your error, the documentation helps you with that: The loc method is used to access elements and not to create them. If an element is not accessible a key error is returned.
