load linearized model directly from file (OpenModelica#213)

Author: arun3688

OMPython/__init__.py

@@ -55,6 +55,7 @@ class which means it will use OMCSessionZMQ by default. If you want to use
 from collections import OrderedDict
 import numpy as np
 import pyparsing
+import importlib
 
 
 if sys.platform == 'darwin':
@@ -1766,11 +1767,10 @@ def linearize(self, lintime = None, simflags= None):  # 22
             # this function is called from the generated python code linearized_model.py at runtime,
             # to improve the performance by directly reading the matrices A, B, C and D from the julia code and avoid building the linearized modelica model
             try:
-                ## add the generated linearfile directory to system path, as running from script does not find the module
+                ## do not add the linearfile directory to path, as multiple execution of linearization will always use the first added path, instead execute the file
                 ## https://github.com/OpenModelica/OMPython/issues/196
-                sys.path.append(os.path.dirname(linearFile))
-                from linearized_model import linearized_model
-                result = linearized_model()
+                module = importlib.machinery.SourceFileLoader("linearized_model", linearFile).load_module()
+                result = module.linearized_model()
                 (n, m, p, x0, u0, A, B, C, D, stateVars, inputVars, outputVars) = result
                 self.linearinputs = inputVars
                 self.linearoutputs = outputVars