As dagw said, if your inner loops aren't inside a .pyx file, then Cython can do little to help. Even if there are, if it involves lots of fiddling with data str

As dagw said, if your inner loops aren't inside a .pyx file, then Cython can do little to help. Even if there are, if it involves lots of fiddling with data structures like dicts and lists, or making use of dynamic or high level features of Python like generators or classes or list comprehensions, then Cython would provide only a small speed increase (say, 20%), because almost all the running time will be spent inside the Python runtime. To get the biggest speed ups out of Cython you need to write C-like code with type annotations. E.g. "for x in range(...):" loops.