Use None instead of empty list in constructors

doc/docs/Python_User_Interface.md

@@ -89,18 +89,18 @@ control various parameters of the Meep computation.
 def __init__(self,
              cell_size,
              resolution,
-             geometry=[],
-             sources=[],
+             geometry=None,
+             sources=None,
              eps_averaging=True,
              dimensions=3,
-             boundary_layers=[],
-             symmetries=[],
+             boundary_layers=None,
+             symmetries=None,
              force_complex_fields=False,
              default_material=Medium(),
              m=0,
              k_point=False,
              kz_2d='complex',
-             extra_materials=[],
+             extra_materials=None,
              material_function=None,
              epsilon_func=None,
              epsilon_input_file='',
@@ -4216,8 +4216,8 @@ def __init__(self,
              epsilon_offdiag=Vector3<0.0, 0.0, 0.0>,
              mu_diag=Vector3<1.0, 1.0, 1.0>,
              mu_offdiag=Vector3<0.0, 0.0, 0.0>,
-             E_susceptibilities=[],
-             H_susceptibilities=[],
+             E_susceptibilities=None,
+             H_susceptibilities=None,
              E_chi2_diag=Vector3<0.0, 0.0, 0.0>,
              E_chi3_diag=Vector3<0.0, 0.0, 0.0>,
              H_chi2_diag=Vector3<0.0, 0.0, 0.0>,
@@ -4638,8 +4638,8 @@ Absorption](Materials.md#saturable-gain-and-absorption).
 
 ```python
 def __init__(self,
-             initial_populations=[],
-             transitions=[],
+             initial_populations=None,
+             transitions=None,
              **kwargs):
 ```
 

python/geom.py

@@ -313,8 +313,8 @@ def __init__(self, epsilon_diag=Vector3(1, 1, 1),
                  epsilon_offdiag=Vector3(),
                  mu_diag=Vector3(1, 1, 1),
                  mu_offdiag=Vector3(),
-                 E_susceptibilities=[],
-                 H_susceptibilities=[],
+                 E_susceptibilities=None,
+                 H_susceptibilities=None,
                  E_chi2_diag=Vector3(),
                  E_chi3_diag=Vector3(),
                  H_chi2_diag=Vector3(),
@@ -425,8 +425,8 @@ def __init__(self, epsilon_diag=Vector3(1, 1, 1),
         self.epsilon_offdiag = Vector3(*epsilon_offdiag)
         self.mu_diag = Vector3(*mu_diag)
         self.mu_offdiag = Vector3(*mu_offdiag)
-        self.E_susceptibilities = E_susceptibilities
-        self.H_susceptibilities = H_susceptibilities
+        self.E_susceptibilities = E_susceptibilities if E_susceptibilities else []
+        self.H_susceptibilities = H_susceptibilities if H_susceptibilities else []
         self.E_chi2_diag = Vector3(chi2, chi2, chi2) if chi2 else Vector3(*E_chi2_diag)
         self.E_chi3_diag = Vector3(chi3, chi3, chi3) if chi3 else Vector3(*E_chi3_diag)
         self.H_chi2_diag = Vector3(*H_chi2_diag)
@@ -842,10 +842,10 @@ class MultilevelAtom(Susceptibility):
     atomic level. See [Materials/Saturable Gain and
     Absorption](Materials.md#saturable-gain-and-absorption).
     """
-    def __init__(self, initial_populations=[], transitions=[], **kwargs):
+    def __init__(self, initial_populations=None, transitions=None, **kwargs):
         super(MultilevelAtom, self).__init__(**kwargs)
-        self.initial_populations = initial_populations
-        self.transitions = transitions
+        self.initial_populations = initial_populations if initial_populations else []
+        self.transitions = transitions if transitions else []
 
 
 class Transition(object):

python/simulation.py

@@ -935,18 +935,18 @@ class Simulation(object):
     def __init__(self,
                  cell_size,
                  resolution,
-                 geometry=[],
-                 sources=[],
+                 geometry=None,
+                 sources=None,
                  eps_averaging=True,
                  dimensions=3,
-                 boundary_layers=[],
-                 symmetries=[],
+                 boundary_layers=None,
+                 symmetries=None,
                  force_complex_fields=False,
                  default_material=mp.Medium(),
                  m=0,
                  k_point=False,
                  kz_2d="complex",
-                 extra_materials=[],
+                 extra_materials=None,
                  material_function=None,
                  epsilon_func=None,
                  epsilon_input_file='',
@@ -1198,20 +1198,20 @@ def __init__(self,
         """
 
         self.cell_size = Vector3(*cell_size)
-        self.geometry = geometry
-        self.sources = sources
+        self.geometry = geometry if geometry else []
+        self.sources = sources if sources else []
         self.resolution = resolution
         self.dimensions = dimensions
-        self.boundary_layers = boundary_layers
-        self.symmetries = symmetries
+        self.boundary_layers = boundary_layers if boundary_layers else []
+        self.symmetries = symmetries if symmetries else []
         self.geometry_center = Vector3(*geometry_center)
         self.eps_averaging = eps_averaging
         self.subpixel_tol = subpixel_tol
         self.subpixel_maxeval = subpixel_maxeval
         self.loop_tile_base_db = loop_tile_base_db
         self.loop_tile_base_eh = loop_tile_base_eh
         self.ensure_periodicity = ensure_periodicity
-        self.extra_materials = extra_materials
+        self.extra_materials = extra_materials if extra_materials else []
         self.default_material = default_material
         self.epsilon_input_file = epsilon_input_file
         self.num_chunks = chunk_layout.numchunks() if isinstance(chunk_layout,mp.BinaryPartition) else num_chunks

python/solver.py

@@ -86,9 +86,9 @@ def __init__(self,
                  target_freq=0.0,
                  tolerance=1.0e-7,
                  num_bands=1,
-                 k_points=[],
+                 k_points=None,
                  ensure_periodicity=True,
-                 geometry=[],
+                 geometry=None,
                  geometry_lattice=mp.Lattice(),
                  geometry_center=mp.Vector3(0, 0, 0),
                  default_material=mp.Medium(epsilon=1),
@@ -104,8 +104,8 @@ def __init__(self,
         self.mode_solver = None
         self.resolution = resolution
         self.eigensolver_flags = eigensolver_flags
-        self.k_points = k_points
-        self.geometry = geometry
+        self.k_points = k_points if k_points else []
+        self.geometry = geometry if geometry else []
         self.geometry_lattice = geometry_lattice
         self.geometry_center = mp.Vector3(*geometry_center)
         self.default_material = default_material