How to map a function using multiple columns in pandas?

Use pd.DataFrame.apply(), as below:

df['d'] = df.apply(lambda x: some_func(a = x['a'], b = x['b'], c = x['c']), axis=1)

NOTE: As @ashishsingal asked about columns, the axis argument should be provided with a value of 1, as the default is 0 (as in the documentation and copied below).

axis : {0 or ‘index’, 1 or ‘columns’}, default 0

• 0 or ‘index’: apply function to each column
• or ‘columns’: apply function to each row