Alternative to scipy and numpy for linear algebra?
I sometimes have this problem..not sure if this works but I often install it using my own account then try to run it in an IDE(komodo in my case) and it doesn't work. Like your issue it says it cannot find it. The way I solve this is to use sudo -i to get into root and then install it from there.
If that does not work can you update your answer to provide a bit more info about the type of system your using(linux, mac, windows), version of python/numpy and how your accessing it so it'll be easier to help.
Is there a good (small and light) alternative to numpy for python, to do linear algebra?
I only need matrices (multiplication, addition), inverses, transposes and such.
Why?

I am tired of trying to install numpy/scipy - it is such a pita to get
  it to work - it never seems to install correctly (esp. since I have
  two machines, one linux and one windows): no matter what I do: compile
  it or install from pre-built binaries. How hard is it to make a
  "normal" installer that just works?