Fix ModelicaSystem cannot load from relative path

OMPython/__init__.py

@@ -29,6 +29,7 @@
 import pyparsing
 import importlib
 import zmq
+import pathlib
 
 
 if sys.platform == 'darwin':
@@ -700,7 +701,7 @@ def __init__(self, fileName=None, modelName=None, lmodel=None, commandLineOption
         self.xmlFile = None
         self.lmodel = lmodel  # may be needed if model is derived from other model
         self.modelName = modelName  # Model class name
-        self.fileName = fileName  # Model file/package name
+        self.fileName = pathlib.Path(fileName).resolve() if fileName is not None else None  # Model file/package name
         self.inputFlag = False  # for model with input quantity
         self.simulationFlag = False  # if the model is simulated?
         self.outputFlag = False
@@ -710,8 +711,8 @@ def __init__(self, fileName=None, modelName=None, lmodel=None, commandLineOption
 
         self._raiseerrors = raiseerrors
 
-        if fileName is not None and not os.path.exists(self.fileName):  # if file does not exist
-            raise IOError("File Error:" + os.path.abspath(self.fileName) + " does not exist!!!")
+        if fileName is not None and not self.fileName.is_file():  # if file does not exist
+            raise IOError(f"File Error: {self.fileName} does not exist!!!")
 
         # set default command Line Options for linearization as
         # linearize() will use the simulation executable and runtime
@@ -741,8 +742,7 @@ def setCommandLineOptions(self, commandLineOptions: str):
 
     def loadFile(self):
         # load file
-        loadFileExp = "".join(["loadFile(", "\"", self.fileName, "\"", ")"]).replace("\\", "/")
-        loadMsg = self.sendExpression(loadFileExp)
+        loadMsg = self.sendExpression(f'loadFile("{self.fileName.as_posix()}")')
         # Show notification or warnings to the user when verbose=True OR if some error occurred i.e., not result
         if self._verbose or not loadMsg:
             self._check_error()

tests/test_ModelicaSystem.py

@@ -3,6 +3,7 @@
 import tempfile
 import shutil
 import os
+import pathlib
 
 
 class ModelicaSystemTester(unittest.TestCase):
@@ -76,6 +77,29 @@ def test_setSimulationOptions(self):
         assert d["stopTime"] == "2.1"
         assert d["tolerance"] == "1.2e-08"
 
+    def test_relative_path(self):
+        cwd = pathlib.Path.cwd()
+        (fd, name) = tempfile.mkstemp(dir=cwd, text=True)
+        try:
+            with os.fdopen(fd, 'w') as f:
+                f.write("""model M
+  Real x(start = 1, fixed=true);
+  parameter Real a = -1;
+equation
+  der(x) = x*a;
+end M;
+""")
+
+            model_file = pathlib.Path(name).relative_to(cwd)
+            model_relative = str(model_file)
+            assert "/" not in model_relative
+
+            mod = OMPython.ModelicaSystem(model_relative, "M", raiseerrors=True)
+            assert float(mod.getParameters("a")[0]) == -1
+        finally:
+            # clean up the temporary file
+            model_file.unlink()
+
 
 if __name__ == '__main__':
     unittest.main()