did the same for Materials Exports and Traps

festim/concentration/traps/traps.py

@@ -10,9 +10,12 @@ class Traps(list):
 
     def __init__(self, *args):
         # checks that input is list
-        if not isinstance(*args, list):
-            raise TypeError("festim.Traps must be a list")
-        super().__init__(self._validate_trap(item) for item in args[0])
+        if len(args) == 0:
+            super().__init__()
+        else:
+            if not isinstance(*args, list):
+                raise TypeError("festim.Traps must be a list")
+            super().__init__(self._validate_trap(item) for item in args[0])
 
         self.F = None
         self.extrinsic_formulations = []

festim/exports/exports.py

@@ -10,9 +10,12 @@ class Exports(list):
 
     def __init__(self, *args):
         # checks that input is list
-        if not isinstance(*args, list):
-            raise TypeError("festim.Exports must be a list")
-        super().__init__(self._validate_export(item) for item in args[0])
+        if len(args) == 0:
+            super().__init__()
+        else:
+            if not isinstance(*args, list):
+                raise TypeError("festim.Exports must be a list")
+            super().__init__(self._validate_export(item) for item in args[0])
 
         self.t = None
         self.V_DG1 = None

festim/materials/materials.py

@@ -15,9 +15,12 @@ class Materials(list):
 
     def __init__(self, *args):
         # checks that input is list
-        if not isinstance(*args, list):
-            raise TypeError("festim.Materials must be a list")
-        super().__init__(self._validate_material(item) for item in args[0])
+        if len(args) == 0:
+            super().__init__()
+        else:
+            if not isinstance(*args, list):
+                raise TypeError("festim.Materials must be a list")
+            super().__init__(self._validate_material(item) for item in args[0])
 
         self.D = None
         self.S = None

test/unit/test_exports/test_exports.py

@@ -131,3 +131,11 @@ def test_set_exports_list_wrong_type(self):
             match="exports must be a list of festim.Export",
         ):
             self.my_exports.exports = [self.my_export, 1]
+
+
+def test_instanciate_with_no_elements():
+    """
+    Test to catch bug described in issue #724
+    """
+    # define exports
+    festim.Exports()

test/unit/test_materials.py

@@ -438,3 +438,11 @@ def test_set_materials_list_wrong_type(self):
             match="materials must be a list of festim.Material",
         ):
             self.my_mats.materials = [self.my_mat, 1]
+
+
+def test_instanciate_with_no_elements():
+    """
+    Test to catch bug described in issue #724
+    """
+    # define exports
+    F.Materials()

test/unit/test_traps/test_traps.py

@@ -240,3 +240,11 @@ def test_set_traps_list_wrong_type(self):
             match="traps must be a list of festim.Trap",
         ):
             self.my_traps.traps = [self.my_trap, 1]
+
+
+def test_instanciate_with_no_elements():
+    """
+    Test to catch bug described in issue #724
+    """
+    # define exports
+    festim.Traps()