A shape calculator for the p-block

You will finish a program that finds the shape of a molecule or ion from the valence electrons of the central atom, the atoms bonded to it and the charge.

The idea. The central atom gives one electron to each hydrogen or halogen atom, and two to each oxygen atom that has a double bond. The electrons that are left form lone pairs, and a negative charge adds electrons. The steric number and the number of lone pairs give the shape.

Your tasks.

1. Complete lone_pairs(valence, ligands, charge) so that it returns the number of lone pairs.
2. Complete steric_number(valence, ligands, charge) so that it returns the number of bonded atoms plus the lone pairs.
3. Complete shape(valence, ligands, charge) so that it returns the name from the table SHAPES.