pygtk present but import failed
> Using default library and include directories for Tcl and Tk because a
> Tk window failed to open. You may need to define DISPLAY for Tk to work
> so that setup can determine where your libraries are located.
> (setup.py:31070): Gtk-WARNING **: cannot open display:
This looks like an X11 issue. Make sure you log in with ssh -X and
that you can launch an X11 app from the build machine in the build
environment. Sometimes you also need to set xhost. Eg if you are
building as root, make sure you can launch an xterm as root before
trying to install matplotlib.