Cell potentials from a table

You will write functions that work with a table of standard potentials. One finds the cell potential of two half-cells. One says whether a cell works. You will also find the best pair of electrodes in the table.

The idea. $E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$. A cell works when this is positive.

Your tasks.

1. Complete cell_potential(cathode, anode) so that it returns the cell potential in volts.
2. Complete works(cathode, anode) so that it returns True when the cell potential is positive.
3. Set best to the pair (cathode, anode) that gives the largest cell potential of all.