adding these together results in na values in the locations that don' overlapin [ ]df df out[ ] nan nan nan nan nan nan nan nan using the add method on df pass df and an argument to fill_valuein [ ]df add(df fill_value= out[ ] relatedlywhen reindexing series or dataframeyou can also specify different fill valuein [ ]df reindex(columns=df columnsfill_value= out[ ] table - flexible arithmetic methods method description add method for addition (+sub method for subtraction (-div method for division (/mul method for multiplication (*operations between dataframe and series as with numpy arraysarithmetic between dataframe and series is well-defined firstas motivating exampleconsider the difference between array and one of its rowsin [ ]arr np arange( reshape(( )in [ ]arr out[ ]array([ ] ] getting started with pandas www it-ebooks info