Merge pull request #35 from rkingsbury/HOH

Solution: enable passing EOS instance as engine

src/pyEQL/engines.py

@@ -391,7 +391,7 @@ def get_osmotic_coefficient(self, solution):
         # coefficient
         for item in salts_dict:
             # ignore HOH in the salt list
-            if item == "HOH":
+            if item.formula == "HOH":
                 continue
 
             # determine alpha1 and alpha2 based on the type of salt

src/pyEQL/solution.py

@@ -45,7 +45,7 @@ def __init__(
         pH: float = 7,
         pE: float = 8.5,
         solvent: str | list = "H2O",
-        engine: Literal["native", "ideal"] = "native",
+        engine: EOS | Literal["native", "ideal"] = "native",
         database: str | Path | Store | None = None,
     ):
         """
@@ -147,8 +147,10 @@ def __init__(
         # set the equation of state engine
         self._engine = engine
         # self.engine: Optional[EOS] = None
-        if self._engine == "ideal":
-            self.engine: EOS = IdealEOS()
+        if isinstance(self._engine, EOS):
+            self.engine: EOS = self._engine
+        elif self._engine == "ideal":
+            self.engine = IdealEOS()
         elif self._engine == "native":
             self.engine = NativeEOS()
         else:

tests/test_solution.py

@@ -9,6 +9,7 @@
 import numpy as np
 import pytest
 from pyEQL import Solution, ureg
+from pyEQL.engines import IdealEOS, NativeEOS
 
 
 @pytest.fixture()
@@ -88,6 +89,23 @@ def test_init_raises():
         Solution(solvent=["D2O", "MeOH"])
 
 
+def test_init_engines():
+    """
+    Test passing an EOS instance as well as the ideal and native EOS
+    """
+    ideal = IdealEOS()
+    s = Solution([["Na+", "4 mol/L"], ["Cl-", "4 mol/L"]], engine=ideal)
+    assert s.engine == ideal
+    s = Solution([["Na+", "4 mol/L"], ["Cl-", "4 mol/L"]], engine="ideal")
+    assert isinstance(s.engine, IdealEOS)
+    assert s.get_activity_coefficient("Na+").magnitude == 1
+    assert s.get_osmotic_coefficient().magnitude == 1
+    s = Solution([["Na+", "4 mol/L"], ["Cl-", "4 mol/L"]], engine="native")
+    assert isinstance(s.engine, NativeEOS)
+    assert s.get_activity_coefficient("Na+").magnitude < 1
+    assert s.get_osmotic_coefficient().magnitude != 1
+
+
 # create an empty and test solutions with the same volume using substance / volume,
 # substance/mass, and substance units
 def test_solute_addition(s2, s3, s4):