>>> from qualitat import mitjanes_districte

>>> lectures = {
...     'E01': [42, 55, 61, 100], 'E02': [30, 34, 50],
...     'E03': [70, 65, 80, 75], 'E04': [51, 49, 53],
...     'E05': [20, 30, 40, 90] }

>>> estacions = {
...     'E01': ('EIXAMPLE', 'A'), 'E02': ('GRACIA', 'A'),
...     'E03': ('EIXAMPLE', 'B'), 'E04': ('SANTS', 'C'),
...     'E05': ('GRACIA', 'A') }

>>> dres = mitjanes_districte(lectures, estacions, 'A')
>>> dres == {
...     'EIXAMPLE': [(64.5, 58.0)],
...     'GRACIA': [(38.0, 34.0), (45.0, 35.0)]
... }
True

>>> mitjanes_districte(lectures, estacions, 'D')
{}

>>> lectures2 = {
...     'E01': [10, 20, 30, 40, 100],
...     'E02': [5, 15, 25],
...     'E03': [60, 70, 80, 90],
...     'E04': [12, 18, 24, 30, 60],
...     'E05': [20, 40, 60, 80, 200],
...     'E06': [7, 9, 11, 13],
...     'E07': [31, 33, 35, 37, 80]
... }
>>> estacions2 = {
...     'E01': ('EIXAMPLE', 'A'), 'E02': ('GRACIA', 'B'),
...     'E03': ('EIXAMPLE', 'A'), 'E04': ('SANTS', 'A'),
...     'E05': ('GRACIA', 'A'), 'E06': ('HORTA', 'C'),
...     'E07': ('SANTS', 'A')
... }
>>> dres = mitjanes_districte(lectures2, estacions2, 'A')
>>> dres == {
...     'EIXAMPLE': [(40.0, 30.0), (75.0, 75.0)],
...     'SANTS': [(28.8, 24.0), (43.2, 35.0)],
...     'GRACIA': [(80.0, 60.0)]
... }
True