corrected the nx,ny,nz confirmation

fipy/meshes/grid1D.py

@@ -1,4 +1,4 @@
 from __future__ import unicode_literals
 from fipy.meshes.nonUniformGrid1D import NonUniformGrid1D as Grid1D
 import warnings
-warnings.warn("Grid1D has been deprecated use NonUniformGrid1D instead.", stacklevel=3)
+warnings.warn("Grid1D has been deprecated use NonUniformGrid1D instead.", stacklevel=3)

fipy/meshes/nonUniformGrid1D.py

@@ -38,6 +38,9 @@ def __init__(self, dx=1., nx=None, overlap=2,
                  _BuilderClass=_NonuniformGrid1DBuilder,
                  _RepresentationClass=_Grid1DRepresentation,
                  _TopologyClass=_Grid1DTopology):
+
+        if not isinstance(nx, int) or nx < 0:
+            raise ValueError("nx must be a non-negative integer")
 
         builder = _BuilderClass()
 

fipy/meshes/nonUniformGrid2D.py

@@ -22,6 +22,8 @@ class NonUniformGrid2D(Mesh2D):
     """
     def __init__(self, dx=1., dy=1., nx=None, ny=None, overlap=2, communicator=parallelComm,
                  _RepresentationClass=_Grid2DRepresentation, _TopologyClass=_Grid2DTopology):
+        if (not isinstance(nx, int) or nx < 0) and (not isinstance(ny, int) or ny < 0):
+            raise ValueError("nx must be a non-negative integer")
 
         builder = _NonuniformGrid2DBuilder()
 

fipy/meshes/nonUniformGrid3D.py

@@ -32,6 +32,9 @@ class NonUniformGrid3D(Mesh):
     def __init__(self, dx = 1., dy = 1., dz = 1., nx = None, ny = None, nz = None, overlap=2, communicator=parallelComm,
                  _RepresentationClass=_Grid3DRepresentation, _TopologyClass=_Grid3DTopology):
 
+        if (not isinstance(nx, int) or nx < 0) and (not isinstance(ny, int) or ny < 0) and (not isinstance(nz, int) or nz < 0):
+            raise ValueError("nx must be a non-negative integer")
+
         builder = _NonuniformGrid3DBuilder()
 
         self.args = {