Answer to Question #316798 in Python for Vice

Question

If df is a DataFrame that includes a column 'x', what is NOT a way to add a new column 'y', using a function 'f' that applies a transformation?

Select an answer:

• df.y = f(df.x)
• df['y'] = None; df.y = f(df.x)
• df['y'] = f(df['x'])
• df = df.assign(y = f(df.x))

Answer 1

df.y = f(df.x)

Pandas doesn't allow columns to be created via a new attribute name. So, pandas sees `y` as an attribute of the dataframe `df` rather than a new column name.