Psyco is a kind of just-in-time (JIT) compiler, a little bit like what exists
for other languages, that emit machine code on the fly instead of interpreting
your Python program step by step. The difference with the traditional approach
to JIT compilers is that Psyco writes several version of the same blocks
(a block is a bit of a function), which are optimized by being specialized to
some kinds of variables (a "kind" can mean a type, but it is more general). The
result is that your unmodified Python programs run faster.