Get length of polyline

Is there a magical way to get the total length of a polyline?
It has to work with rounded corners. I only have one polyline per layer if that makes it easier.

At the moment I use normal lines which I calculate the total length of by using their coordinates (they lack the rounded corners though).

dxflib is solely designed to parse / write DXF files. Any kind of data interpretation or analysis has to be done on top of it. QCAD for example has a tool to get the total length of all selected entities.