This is not a bug. Please read about references in Python, and what this
means:



py> b=[0]
py> a=[b,b]
py> a[0] is a[1]
True
py> c=[[0],[0]]
py> c[0] is c[1]
False
py> c[0] == c[1]
True

In short, there is only a single list stored in the variable gridRow,
and the very same list is appended multiple times (not copies of the
list, but the very same object). There are then multiple ways to refer
to the list, such as g[0] or g[1].

To avoid sharing the list objects, either create new lists (i.e. nest
the first loop into the second one, and create a new gridRow on each
outer loop iteration), or create clones of the first list, e.g.

  grid.append(list(gridRow))
# or
  grid.append(gridRow[:])