How to use the barril.units function in barril

def GetQuantity(unit="cm"):
    return units.ObtainQuantity(unit, "well-length")

def testFormatting(unit_database_start_units):
    point = units.FixedArray(2, "length", [(100, 150), (50, 50)], "m")
    assert "(100, 150) (50, 50) [m]" == str(point)

def MakeFixedArray(values):
    """Creates a fixed array with 3 dimensions used by testScalarOperations"""
    return units.FixedArray(3, "length", values, "m")

def testPoscWithoutFillCategories(unit_database_posc_len_no_category):
    unit_database = unit_database_posc_len_no_category

    unit_database.AddCategory("my_len", "length")

    # this category does not exist because we didn't fill the categories
    with pytest.raises(UnitsError):
        units.Scalar("length", 100, "km")

    u1 = units.Scalar("my_len", 100, "km")
    u2 = units.Scalar("my_len", 100000, "m")
    assert approx(abs(u1.value - u2.GetValue("km")), 7) == 0

def db():
    db = units.UnitDatabase.GetSingleton()
    yield db

def testPoscLength(unit_database_posc):
    # 'length'
    u1 = units.Scalar("length", 10, "ft")
    u2 = units.Scalar("length", 100, "km")
    u3 = units.Scalar("length", 15, "yd")
    u4 = units.Scalar("length", 15, "yd")
    assert u1.GetQuantityType() == u2.GetQuantityType()
    assert u1.unit != u2.unit
    assert u3 == u4
    # u1.unit = 'm'  # from feet to metres
    assert approx(abs(u1.GetValue("m") - 3.048), 7) == 0
    # u2.unit = 'm'  # from kilometres to metres
    assert approx(abs(u2.GetValue("m") - 100000.0), 7) == 0
    # u3.unit = 'ft'  # from yd to ft
    assert approx(abs(u3.GetValue("ft") - 45.0), 7) == 0
    # now return u3.unit from feet to yards and compare u3.value with u4.value
    # sanity-check
    assert u3.GetValue("yd") == u4.value

def testQuantity(unit_database_well_length):
    Quantity("well-length", "m")
    with pytest.raises(units.InvalidQuantityTypeError):
        Quantity("foo", "m")

def CreateUnitDatabaseLenTemp():
    """
    :rtype: UnitDatabase
    :returns:
        Returns a unit database with length and time quantity types
    """
    unit_database = units.UnitDatabase()

    unit_database.AddUnitBase("length", "meters", "m")
    unit_database.AddUnit("length", "kilometers", "km", "%f / 1000.0", "%f * 1000.0")
    unit_database.AddUnitBase("temperature", "degC", "degC")
    unit_database.AddUnit(
        "temperature", "Kelvin", "K", "%f + 270", "%f - 270"
    )  # not correct convertion on purpose (for testing only)

    unit_database.AddCategory("length", "length")
    unit_database.AddCategory("temperature", "temperature")

    return unit_database

def CreateUnitDatabaseLenPressure():
    """
    :rtype: UnitDatabase
    :returns:
        Returns a unit database with length and time quantity types
    """
    unit_database = units.UnitDatabase()

    unit_database.AddUnitBase("length", "meters", "m")
    unit_database.AddUnit("length", "kilometers", "km", "%f / 1000.0", "%f * 1000.0")
    unit_database.AddUnitBase("pressure", "pascal", "Pa")
    unit_database.AddUnit(
        "pressure", "pounds/square inch", "psi", "%f / 6894.757", "%f * 6894.757"
    )

    unit_database.AddCategory("length", "length")
    unit_database.AddCategory("pressure", "pressure")

    return unit_database