Including Canada makes all the difference!

Take a look at Metakit. http://www.equi4.com/metakit/index.html. Its single file, small, fast and it has proven itself over many years. It is written in C++ and bindings for Python and Tcl are available. Instead of tables, rows and fields it uses similar concepts called view, index and property. Interestingly, a property may also be a subview thus allowing a mix of a relational database (flexible) and a hierarchical database (fast).