When using a pandas dataframe, how do I add column if does not exist?

Question

I\'m new to using pandas and am writing a script where I read in a dataframe and then do some computation on some of the columns.

Sometimes I will have the column called

Answer 1

If you were creating the dataframe from scratch, you could create the missing columns without a loop merely by passing the column names into the pd.DataFrame() call:

cols = ['column 1','column 2','column 3','column 4','column 5']
df = pd.DataFrame(list_or_dict, index=['a',], columns=cols)