Use additive dispersion

src/elli/dispersions/base_dispersion.py

@@ -73,6 +73,21 @@ def __init__(self, *args, **kwargs):
             self.single_params_template, *args, **kwargs
         )
 
+    summation_error_message = ""
+
+    def __radd__(self, other: Union[int, float, "Dispersion"]) -> "Dispersion":
+        return self.__add__(other)
+
+    def __add__(
+        self, other: Union[int, float, "AdditiveDispersion"]
+    ) -> "AdditiveDispersion":
+        raise TypeError(
+            f"unsupported operand type(s) for +: {type(self)} and {type(other)}."
+            f"\n{self.summation_error_message}"
+            if self.summation_error_message
+            else ""
+        )
+
     @abstractmethod
     def dielectric_function(self, lbda: npt.ArrayLike) -> npt.NDArray:
         """Calculates the dielectric function in a given wavelength window.
@@ -101,26 +116,6 @@ def add(self, *args, **kwargs) -> "Dispersion":
 
         return self
 
-    def __radd__(self, other: Union[int, float, "Dispersion"]) -> "Dispersion":
-        """Add up the dielectric function of multiple models"""
-        return self.__add__(other)
-
-    def __add__(self, other: Union[int, float, "Dispersion"]) -> "Dispersion":
-        """Add up the dielectric function of multiple models"""
-        if isinstance(other, UnsummableDispersion):
-            other.__add__(self)
-
-        if isinstance(other, DispersionSum):
-            return other.__add__(self)
-
-        if isinstance(other, (int, float)):
-            return DispersionSum(self, dispersions.EpsilonInf(eps=other))
-
-        if not isinstance(other, Dispersion):
-            raise TypeError(f"Invalid type {type(other)} added to dispersion")
-
-        return DispersionSum(self, other)
-
     def get_dielectric(self, lbda: npt.ArrayLike) -> npt.NDArray:
         """Returns the dielectric constant for wavelength 'lbda' default unit (nm)
         in the convention ε1 + iε2."""
@@ -205,17 +200,31 @@ def _dict_to_str(dic):
         )
 
 
-class UnsummableDispersion(Dispersion):
-    """This denotes a dispersion which is not summable"""
+class AdditiveDispersion(Dispersion):
+    """An additive dispersion"""
 
-    @property
-    @abstractmethod
-    def summation_error_message(self):
-        """The message being displayed when someone tries
-        to perform an addition with this dispersion."""
+    def __add__(self, other: Union[int, float, "Dispersion"]) -> "DispersionSum":
+        """Add up the dielectric function of multiple models"""
+        if not isinstance(other, Dispersion) and not isinstance(other, (int, float)):
+            raise TypeError(
+                f"unsupported operand type(s) for +: '{type(self)}' and '{type(other)}'"
+            )
 
-    def __add__(self, _: Union[int, float, "Dispersion"]) -> "Dispersion":
-        raise ValueError(self.summation_error_message)
+        if isinstance(self, DispersionSum) and isinstance(other, DispersionSum):
+            self.dispersions += other.dispersions  # pylint: disable=no-member
+            return self
+
+        if isinstance(self, AdditiveDispersion) and isinstance(other, DispersionSum):
+            other.dispersions.append(self)
+            return other
+
+        if isinstance(other, (int, float)):
+            return DispersionSum(self, dispersions.EpsilonInf(eps=other))
+
+        if not isinstance(other, AdditiveDispersion):
+            other.__add__(self)
+
+        return DispersionSum(self, other)
 
 
 class DispersionFactory:
@@ -240,31 +249,16 @@ def get_dispersion(identifier: str, *args, **kwargs) -> Dispersion:
         raise ValueError(f"No such dispersion: {identifier}")
 
 
-class DispersionSum(Dispersion):
+class DispersionSum(AdditiveDispersion):
     """Represents a sum of two dispersions"""
 
     single_params_template = {}
     rep_params_template = {}
 
-    def __init__(self, *disps: Dispersion) -> None:
+    def __init__(self, *disps: AdditiveDispersion) -> None:
         super().__init__()
         self.dispersions = disps
 
-    def __add__(self, other: Union[int, float, "Dispersion"]) -> "Dispersion":
-        if isinstance(other, UnsummableDispersion):
-            other.__add__(self)
-
-        if isinstance(other, DispersionSum):
-            self.dispersions += other.dispersions
-            return self
-
-        if isinstance(other, (int, float)):
-            self.dispersions.append(dispersions.EpsilonInf(eps=other))
-            return self
-
-        self.dispersions.append(other)
-        return self
-
     def dielectric_function(self, lbda: npt.ArrayLike) -> npt.NDArray:
         dielectric_function = sum(
             disp.dielectric_function(lbda) for disp in self.dispersions

src/elli/dispersions/cauchy.py

@@ -2,10 +2,10 @@
 """Cauchy dispersion."""
 import numpy.typing as npt
 
-from .base_dispersion import UnsummableDispersion
+from .base_dispersion import Dispersion
 
 
-class Cauchy(UnsummableDispersion):
+class Cauchy(Dispersion):
     r"""Cauchy dispersion.
 
     Single parameters:
@@ -28,7 +28,7 @@ class Cauchy(UnsummableDispersion):
     """
 
     summation_error_message = (
-        "The cauchy dispersion cannot be added to other dispersions. "
+        "The Cauchy dispersion cannot be added to other dispersions. "
         "Try the Poles or Lorentz model instead."
     )
 

src/elli/dispersions/cauchy_custom.py

@@ -2,10 +2,10 @@
 """Cauchy dispersion with custom exponents."""
 import numpy.typing as npt
 
-from .base_dispersion import UnsummableDispersion
+from .base_dispersion import Dispersion
 
 
-class CauchyCustomExponent(UnsummableDispersion):
+class CauchyCustomExponent(Dispersion):
     r"""Cauchy dispersion with custom exponents.
 
     Single parameters:
@@ -22,7 +22,7 @@ class CauchyCustomExponent(UnsummableDispersion):
     """
 
     summation_error_message = (
-        "The cauchy dispersion cannot be added to other dispersions. "
+        "The Cauchy dispersion cannot be added to other dispersions. "
         "Try the Poles or Lorentz model instead."
     )
 

src/elli/dispersions/cody_lorentz.py

@@ -6,11 +6,11 @@
 from scipy.interpolate import interp1d
 
 from ..utils import conversion_wavelength_energy
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 from ..kkr import im2re_reciprocal
 
 
-class CodyLorentz(Dispersion):
+class CodyLorentz(AdditiveDispersion):
     """Tauc-Lorentz dispersion law. Model by Ferlauto et al.
 
     Single parameters:

src/elli/dispersions/constant_refractive_index.py

@@ -2,10 +2,10 @@
 """Constant refractive index."""
 import numpy.typing as npt
 
-from .base_dispersion import UnsummableDispersion
+from .base_dispersion import Dispersion
 
 
-class ConstantRefractiveIndex(UnsummableDispersion):
+class ConstantRefractiveIndex(Dispersion):
     r"""Constant refractive index.
 
     Single parameters:

src/elli/dispersions/drude_energy.py

@@ -3,10 +3,10 @@
 import numpy.typing as npt
 
 from ..utils import conversion_wavelength_energy
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class DrudeEnergy(Dispersion):
+class DrudeEnergy(AdditiveDispersion):
     r"""Drude dispersion model with parameters in units of energy.
     Drude models in the literature typically contain an additional epsilon infinity value.
     Use `EpsilonInf` to add this parameter or simply add a number, e.g. DrudeEnergy() + 2, where

src/elli/dispersions/drude_resistivity.py

@@ -5,10 +5,10 @@
 import scipy.constants as sc
 
 from ..utils import conversion_wavelength_energy
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class DrudeResistivity(Dispersion):
+class DrudeResistivity(AdditiveDispersion):
     r"""Drude dispersion model with resistivity based parameters.
     Drude models in the literature typically contain an additional epsilon infinity value.
     Use `EpsilonInf` to add this parameter or simply do DrudeEnergy() + eps_inf.

src/elli/dispersions/epsilon_inf.py

@@ -2,10 +2,10 @@
 """Constant epsilon infinity."""
 import numpy.typing as npt
 
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class EpsilonInf(Dispersion):
+class EpsilonInf(AdditiveDispersion):
     r"""Constant epsilon infinity.
 
     Single parameters:

src/elli/dispersions/gaussian.py

@@ -8,10 +8,10 @@
 from scipy.special import dawsn
 
 from ..utils import conversion_wavelength_energy
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class Gaussian(Dispersion):
+class Gaussian(AdditiveDispersion):
     r"""Dispersion law with gaussian oscillators.
 
     Single parameters:

src/elli/dispersions/lorentz_energy.py

@@ -3,10 +3,10 @@
 import numpy.typing as npt
 
 from ..utils import conversion_wavelength_energy
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class LorentzEnergy(Dispersion):
+class LorentzEnergy(AdditiveDispersion):
     r"""Lorentz dispersion law with parameters in units of energy.
 
     Single parameters:

src/elli/dispersions/lorentz_lambda.py

@@ -2,10 +2,10 @@
 """Lorentz dispersion law with parameters in units of wavelengths."""
 import numpy.typing as npt
 
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class LorentzLambda(Dispersion):
+class LorentzLambda(AdditiveDispersion):
     r"""Lorentz dispersion law with parameters in units of wavelengths.
 
     Single parameters:

src/elli/dispersions/poles.py

@@ -3,10 +3,10 @@
 import numpy.typing as npt
 
 from ..utils import conversion_wavelength_energy
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class Poles(Dispersion):
+class Poles(AdditiveDispersion):
     r"""Dispersion law for an UV and IR pole,
     i.e. Lorentz oscillators outside the fitting spectral range and zero broadening.
 

src/elli/dispersions/polynomial.py

@@ -2,10 +2,10 @@
 """Polynomial dispersion."""
 import numpy.typing as npt
 
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class Polynomial(Dispersion):
+class Polynomial(AdditiveDispersion):
     r"""Polynomial expression for the dielectric function.
 
     Single parameters:

src/elli/dispersions/sellmeier.py

@@ -2,10 +2,10 @@
 """Sellmeier dispersion."""
 import numpy.typing as npt
 
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class Sellmeier(Dispersion):
+class Sellmeier(AdditiveDispersion):
     r"""Sellmeier dispersion.
 
     Single parameters:

src/elli/dispersions/sellmeier_custom.py

@@ -2,10 +2,10 @@
 """Sellmeier dispersion."""
 import numpy.typing as npt
 
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class SellmeierCustomExponent(Dispersion):
+class SellmeierCustomExponent(AdditiveDispersion):
     r"""Sellmeier dispersion with custom exponents.
 
     Single parameters:

src/elli/dispersions/tanguy.py

@@ -8,10 +8,10 @@
 from scipy.special import digamma, gamma
 
 from ..utils import conversion_wavelength_energy
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class Tanguy(Dispersion):
+class Tanguy(AdditiveDispersion):
     r"""Fractional dimensional Tanguy model.
     This model is an analytical expression of Wannier excitons, including
     bound and unbound states.

src/elli/dispersions/tauc_lorentz.py

@@ -5,10 +5,10 @@
 from numpy.lib.scimath import sqrt
 
 from ..utils import conversion_wavelength_energy
-from .base_dispersion import Dispersion
+from .base_dispersion import AdditiveDispersion
 
 
-class TaucLorentz(Dispersion):
+class TaucLorentz(AdditiveDispersion):
     """Tauc-Lorentz dispersion law. Model by Jellison and Modine.
 
     Single parameters:

tests/test_unsummable_dispersion.py

@@ -6,13 +6,15 @@
 def test_fail_on_adding_cauchy():
     """Test whether the kkr reproduces the analytical expression of Tauc-Lorentz"""
     cauchy_err_str = (
-        "The cauchy dispersion cannot be added to other dispersions. "
+        "unsupported operand type(s) for +: "
+        "<class 'elli.dispersions.cauchy.Cauchy'> and <class 'elli.dispersions.cauchy.Cauchy'>."
+        "\nThe Cauchy dispersion cannot be added to other dispersions. "
         "Try the Poles or Lorentz model instead."
     )
-    with pytest.raises(ValueError) as sum_err:
+    with pytest.raises(TypeError) as sum_err:
         _ = Cauchy() + Cauchy()
 
     assert cauchy_err_str in str(sum_err.value)
 
-    with pytest.raises(ValueError):
+    with pytest.raises(TypeError):
         _ = 1 + Cauchy()