add Solution.from_phreeqc() + tests

src/pyEQL/solution.py

@@ -11,6 +11,7 @@
 import logging
 import os
 import warnings
+import re
 from functools import lru_cache
 from importlib.resources import files
 from pathlib import Path
@@ -2523,6 +2524,66 @@
             return Solution(**solution_dict)
         return loadfn(filename)
 
+
+
+    @classmethod
+    def from_phreeqc(cls, path_to_pqi: str) -> "Solution":
+        """
+        Parse a PHREEQC .pqi input file and pull out only the SOLUTION block,
+        extracting solute amounts (assumed mol/L), plus pH, pE, and temperature if present.
+        """
+        import re
+
+        sol_lines: list[str] = []
+        in_solution = False
+
+        with open(path_to_pqi, "r") as f:
+            for raw in f:
+                line = raw.strip()
+                if not in_solution and line.upper().startswith("SOLUTION"):
+                    in_solution = True
+                    continue
+                # stop on blank or a new ALL-CAPS keyword
+                if in_solution and (line == "" or re.match(r"^[A-Z]+\b", line)):
+                    break
+                if in_solution:
+                    sol_lines.append(line)
+
+        if not sol_lines:
+            raise ValueError(f"No SOLUTION block found in '{path_to_pqi}'")
+
+        composition: dict[str, str] = {}
+        pH = pE = None
+        temperature = None  # degrees C
+
+        for l in sol_lines:
+            parts = re.split(r"\s+", l)
+            key = parts[0].upper()
+            vals = parts[1:]
+            if key == "PH":
+                pH = float(vals[0])
+            elif key == "PE":
+                pE = float(vals[0])
+            elif key in ("TEMP", "TEMPERATURE"):
+                temperature = float(vals[0])
+            else:
+                # solute line: e.g. "Ca+2 0.01"
+                try:
+                    amt = float(vals[0])
+                except ValueError:
+                    continue
+                # **here** we tag the unit so pyEQL knows mol/L
+                composition[parts[0]] = f"{amt} mol/L"
+
+        return cls(
+            solutes=composition,
+            pH=pH,
+            pE=pE,
+            temperature=f"{temperature} degC" if temperature is not None else None,
+            engine="ideal",
+        )
+
+
     # arithmetic operations
     def __add__(self, other: Solution) -> Solution:
         """

tests/test_parser_from_phreeqc.py

@@ -0,0 +1,32 @@
+import warnings
+warnings.filterwarnings("ignore", category=RuntimeWarning)
+
+import textwrap
+import pytest
+
+from pyEQL import Solution
+
+def test_from_phreeqc_minimal_parser(tmp_path):
+    """Smoke-test our new from_phreeqc() on a tiny SOLUTION block."""
+    pqi = tmp_path / "sample.pqi"
+    pqi.write_text(textwrap.dedent("""
+        SOLUTION foo
+          pH 7.5
+          temp 30
+          Ca+2 0.01
+          SO4-2 0.01
+
+        END
+    """))
+    sol = Solution.from_phreeqc(str(pqi))
+    assert sol.pH == pytest.approx(7.5, rel=1e-6)
+    assert sol.temperature.magnitude == pytest.approx(303.15, rel=1e-6)
+    assert sol.get_amount("Ca+2", "mol/L").magnitude == pytest.approx(0.01, rel=1e-6)
+    assert sol.get_amount("SO4-2", "mol/L").magnitude == pytest.approx(0.01, rel=1e-6)
+
+def test_from_phreeqc_missing_block_raises(tmp_path):
+    """If there is no SOLUTION block, we should get a ValueError."""
+    pqi = tmp_path / "empty.pqi"
+    pqi.write_text("THIS FILE HAS NO SOLUTION BLOCK\n")
+    with pytest.raises(ValueError):
+        Solution.from_phreeqc(str(pqi))