I would like to make a buffer for a polyline and get as Output a Polygon with the same angles as the polyline, having not arcs, like in ordinary buffers.
i tried the
FLAT option in arcpy, but it's applied to just the both ends.
You could try the Flat-end line buffer tool. I made it for a specific purpose for which it works fine. I sometimes merge the result to create a polygon from. The tool should work fine with 10.0. Have not tested in 10.1.
EDIT: There is a few parameters that can be set; distance, mitered or beveled, extend line ends. (for my purposes I needed to extend the line ends so i made that an option) Because it was made for specific purpose you should be aware that it does not resolve crossing lines (as I mentioned in my comment above). If anyone is interested I can illustrate what this looks like. Basically, resulting crossing lines have to be resolved manually before creating a polygon or polygon will result in a non-simple geometry.
I thought I would add some visuals to show what this basically does: Result: Result as polygon (also use a custom tool for that):
I have made a function in ArcPy to offset a polyline. Here's the function from my ArcPy script and the result: