>>> from choir import singers_dict

>>> lcant = [('Josefina', 'alto', True), ('Pepet', 'bass', False),
... ('Josep', 'tenor', True), ('Fina', 'soprano', True), 
... ('Pepeta', 'soprano', True), ('Josemari', 'tenor', True),
... ('Mariajo', 'soprano', False), ('Fineta', 'soprano', True),
... ('Xema', 'bass', True), ('Mariajosep', 'alto', True),
... ('Pep', 'tenor', True)]
>>> d = singers_dict(lcant)
>>> if d != {'bass': [2, 1], 'soprano': [4, 3], 'tenor': [3, 3], 'alto': [2, 2]}:
...    print(d)

>>> d = singers_dict(lcant[:5])
>>> if d != {'tenor': [1, 1], 'bass': [1, 0], 'soprano': [2, 2], 'alto': [1, 1]}:
...    print(d)

>>> d = singers_dict([])
>>> if d != {'tenor': [0, 0], 'bass': [0, 0], 'soprano': [0, 0], 'alto': [0, 0]}:
...    print(d)

>>> d = singers_dict(lcant[8:])
>>> if d != {'alto': [1, 1], 'bass': [1, 1], 'soprano': [0, 0], 'tenor': [1, 1]}:
...    print(d)