def get_atomic_weight_for_compound(compound: str) -> float:
"""
This function needs to be implemented.
Given the chemical formula of a compount return it's corresponding
atomic weight.
Chemical formulas are expressed in a very simple grammar.
Element symbols always start with a capital letter, and may have
one or two following characters which are always lowercase, for
example:
* "H" -> Hydrogen
* "He" -> Helium
* "Uuh" -> Ununhexium
Element symbols are followed by an optional number which indicates
how many atoms of a symbol are present in a single molecule of
the substance.
* "O2" -> Two atoms of oxygen
* "H2SO4" -> Two hydrogens, One Sulphur, 4 Oxygens
* "He" -> A single atom of Helium
The number is omitted in the case that there is single atom
of an element in a molecule, hence this is not valid:
* "H2S1O4" -> Invalid because "1" is redundant here.
"""
if not compound:
return 0.0
c = periodic_table.Compound(compound)
return c.weight()
def test_compound_weight_multi_2letter():
c = periodic_table.Compound("Al4O2")
assert c.weight() == 15.999 * 2 + 26.98153857 * 4
def test_compound_weight_multi():
c = periodic_table.Compound("N2O2")
assert c.weight() == 15.999 * 2 + 14.007 * 2
def test_compound_weight_simple():
c = periodic_table.Compound("O2")
assert c.weight() == 15.999 * 2
def test_compound_create_3letter1letter():
c = periodic_table.Compound("CaCl2O")
def test_compound_create_1letter1letternumbered():
c = periodic_table.Compound("N2O2")
def test_compound_create_1letter1letter():
c = periodic_table.Compound("NO")
def test_compound_create_2letter1letter():
"""Use an initial 2 char symbol that
can be confused with a single character one."""
c = periodic_table.Compound("CaC")
def test_compound_create_badchars_end():
with pytest.raises(periodic_table.InvalidFormula):
c = periodic_table.Compound("He,.$£")
def test_compound_create_badchars_beginning():
with pytest.raises(periodic_table.InvalidFormula):
c = periodic_table.Compound(",.$£He")
def test_compound_create_completely_invalid():
with pytest.raises(periodic_table.InvalidFormula):
c = periodic_table.Compound(",.$£")
def test_compound_create_simple_invalid_count_1():
with pytest.raises(periodic_table.InvalidFormula):
c = periodic_table.Compound("O1")
def test_compound_create_simple_numbered():
c = periodic_table.Compound("O2")
def test_compound_create_simple():
c = periodic_table.Compound("O")
def test_compound_create_empty():
c = periodic_table.Compound("")
assert c.weight() == 0.0
