diff --git a/pyro/compressible/simulation.py b/pyro/compressible/simulation.py
index d0bcd6a5a..7b75c573b 100644
--- a/pyro/compressible/simulation.py
+++ b/pyro/compressible/simulation.py
@@ -99,7 +99,7 @@ class Simulation(NullSimulation):
 
     """
 
-    def initialize(self, extra_vars=None, ng=4):
+    def initialize(self, *, extra_vars=None, ng=4):
         """
         Initialize the grid and variables for compressible flow and set
         the initial conditions for the chosen problem.
diff --git a/pyro/compressible_fv4/simulation.py b/pyro/compressible_fv4/simulation.py
index dc5afcbfb..a88d64696 100644
--- a/pyro/compressible_fv4/simulation.py
+++ b/pyro/compressible_fv4/simulation.py
@@ -5,10 +5,11 @@
 
 class Simulation(compressible_rk.Simulation):
 
-    def __init__(self, solver_name, problem_name, rp, timers=None, data_class=fv.FV2d):
+    def __init__(self, solver_name, problem_name, rp, *,
+                 timers=None, data_class=fv.FV2d):
         super().__init__(solver_name, problem_name, rp, timers=timers, data_class=data_class)
 
-    def initialize(self, extra_vars=None, ng=5):
+    def initialize(self, *, extra_vars=None, ng=5):
         super().initialize(extra_vars=extra_vars, ng=ng)
 
     def substep(self, myd):
diff --git a/pyro/compressible_react/simulation.py b/pyro/compressible_react/simulation.py
index 6abaecfa2..0648a0c34 100644
--- a/pyro/compressible_react/simulation.py
+++ b/pyro/compressible_react/simulation.py
@@ -8,7 +8,7 @@
 
 class Simulation(compressible.Simulation):
 
-    def initialize(self, extra_vars=None, ng=4):
+    def initialize(self, *, extra_vars=None, ng=4):
         """
         For the reacting compressible solver, our initialization of
         the data is the same as the compressible solver, but we
diff --git a/pyro/incompressible/simulation.py b/pyro/incompressible/simulation.py
index 714d17835..b7ca0fb64 100644
--- a/pyro/incompressible/simulation.py
+++ b/pyro/incompressible/simulation.py
@@ -15,7 +15,7 @@
 
 class Simulation(burgers_simulation):
 
-    def initialize(self, other_bc=False, aux_vars=()):
+    def initialize(self, *, other_bc=False, aux_vars=()):
         """
         Initialize the grid and variables for incompressible flow and
         set the initial conditions for the chosen problem.
diff --git a/pyro/lm_atm/simulation.py b/pyro/lm_atm/simulation.py
index eb09b10fe..cf0a23c86 100644
--- a/pyro/lm_atm/simulation.py
+++ b/pyro/lm_atm/simulation.py
@@ -12,7 +12,7 @@
 
 
 class Basestate:
-    def __init__(self, ny, ng=0):
+    def __init__(self, ny, *, ng=0):
         self.ny = ny
         self.ng = ng
         self.qy = ny + 2*ng
@@ -37,7 +37,7 @@ def jp(self, shift, buf=0):
 
 class Simulation(NullSimulation):
 
-    def __init__(self, solver_name, problem_name, rp, timers=None):
+    def __init__(self, solver_name, problem_name, rp, *, timers=None):
 
         NullSimulation.__init__(self, solver_name, problem_name, rp, timers=timers)
 
diff --git a/pyro/mesh/boundary.py b/pyro/mesh/boundary.py
index a63482f35..84551e693 100644
--- a/pyro/mesh/boundary.py
+++ b/pyro/mesh/boundary.py
@@ -75,7 +75,7 @@ class BC:
 
     """
 
-    def __init__(self,
+    def __init__(self, *,
                  xlb="outflow", xrb="outflow",
                  ylb="outflow", yrb="outflow",
                  xl_func=None, xr_func=None,
diff --git a/pyro/mesh/patch.py b/pyro/mesh/patch.py
index 1b5d6997b..dcb9aafbb 100644
--- a/pyro/mesh/patch.py
+++ b/pyro/mesh/patch.py
@@ -59,7 +59,7 @@ class Grid2d:
 
     # pylint: disable=too-many-instance-attributes
 
-    def __init__(self, nx, ny, ng=1,
+    def __init__(self, nx, ny, *, ng=1,
                  xmin=0.0, xmax=1.0, ymin=0.0, ymax=1.0):
         """
         Create a Grid2d object.
@@ -146,7 +146,7 @@ def __init__(self, nx, ny, ng=1,
         self.xr2d = ArrayIndexer(d=xr2d, grid=self)
         self.yr2d = ArrayIndexer(d=yr2d, grid=self)
 
-    def scratch_array(self, nvar=1):
+    def scratch_array(self, *, nvar=1):
         """
         return a standard numpy array dimensioned to have the size
         and number of ghostcells as the parent grid
@@ -198,10 +198,10 @@ class Cartesian2d(Grid2d):
     y = y
     """
 
-    def __init__(self, nx, ny, ng=1,
+    def __init__(self, nx, ny, *, ng=1,
                  xmin=0.0, xmax=1.0, ymin=0.0, ymax=1.0):
 
-        super().__init__(nx, ny, ng, xmin, xmax, ymin, ymax)
+        super().__init__(nx, ny, ng=ng, xmin=xmin, xmax=xmax, ymin=ymin, ymax=ymax)
 
         self.coord_type = 0
 
@@ -242,7 +242,7 @@ class SphericalPolar(Grid2d):
     theta = y
     """
 
-    def __init__(self, nx, ny, ng=1,
+    def __init__(self, nx, ny, *, ng=1,
                  xmin=0.2, xmax=1.0, ymin=0.0, ymax=1.0):
 
         # Make sure theta is within [0, PI]
@@ -252,7 +252,7 @@ def __init__(self, nx, ny, ng=1,
         assert xmin - ng*(xmax-xmin)/nx >= 0.0, \
             "xmin (r-direction), must be large enough so ghost cell doesn't have negative x."
 
-        super().__init__(nx, ny, ng, xmin, xmax, ymin, ymax)
+        super().__init__(nx, ny, ng=ng, xmin=xmin, xmax=xmax, ymin=ymin, ymax=ymax)
 
         self.coord_type = 1
 
@@ -332,7 +332,7 @@ class CellCenterData2d:
 
     # pylint: disable=too-many-instance-attributes
 
-    def __init__(self, grid, dtype=np.float64):
+    def __init__(self, grid, *, dtype=np.float64):
 
         """
         Initialize the CellCenterData2d object.
@@ -608,14 +608,14 @@ def fill_BC(self, name):
             except TypeError:
                 bnd.ext_bcs[self.BCs[name].yrb](self.BCs[name].yrb, "yrb", name, self, self.ivars)
 
-    def min(self, name, ng=0):
+    def min(self, name, *, ng=0):
         """
         return the minimum of the variable name in the domain's valid region
         """
         n = self.names.index(name)
         return np.min(self.data.v(buf=ng, n=n))
 
-    def max(self, name, ng=0):
+    def max(self, name, *, ng=0):
         """
         return the maximum of the variable name in the domain's valid region
         """
diff --git a/pyro/pyro_sim.py b/pyro/pyro_sim.py
index a92c7467e..7d265c2e3 100755
--- a/pyro/pyro_sim.py
+++ b/pyro/pyro_sim.py
@@ -36,7 +36,7 @@ class Pyro:
     The main driver to run pyro.
     """
 
-    def __init__(self, solver_name, from_commandline=False):
+    def __init__(self, solver_name, *, from_commandline=False):
         """
         Constructor
 
@@ -280,12 +280,13 @@ def get_sim(self):
 
 
 class PyroBenchmark(Pyro):
-    """
-    A subclass of Pyro for benchmarking. Inherits everything from pyro, but adds benchmarking routines.
+    """A subclass of Pyro for benchmarking. Inherits everything from
+    pyro, but adds benchmarking routines.
+
     """
 
-    def __init__(self, solver_name, comp_bench=False,
-                 reset_bench_on_fail=False, make_bench=False):
+    def __init__(self, solver_name, *,
+                 comp_bench=False, reset_bench_on_fail=False, make_bench=False):
         """
         Constructor
 
diff --git a/pyro/simulation_null.py b/pyro/simulation_null.py
index 7dce37e84..c714117ab 100644
--- a/pyro/simulation_null.py
+++ b/pyro/simulation_null.py
@@ -102,7 +102,8 @@ def bc_setup(rp):
 
 class NullSimulation:
 
-    def __init__(self, solver_name, problem_name, rp, timers=None, data_class=patch.CellCenterData2d):
+    def __init__(self, solver_name, problem_name, rp, *,
+                 timers=None, data_class=patch.CellCenterData2d):
         """
         Initialize the Simulation object
 
diff --git a/pyro/swe/simulation.py b/pyro/swe/simulation.py
index db5327bac..a0bb073bc 100644
--- a/pyro/swe/simulation.py
+++ b/pyro/swe/simulation.py
@@ -93,7 +93,7 @@ class Simulation(NullSimulation):
 
     """
 
-    def initialize(self, extra_vars=None, ng=4):
+    def initialize(self, *, extra_vars=None, ng=4):
         """
         Initialize the grid and variables for swe flow and set
         the initial conditions for the chosen problem.