When you call turtle.shapetransform with a transformation matrix, nothing happens. You have to call turtle.shapesize or turtle.shearfactor first before turtle.shapetransform will take affect. Here is an example.

turtle.shapetransform(2,0,0,2) 
turtle.shapesize(1) 
turtle.shapetransform(2,0,0,2)

Nothing happens with the first call of shapetransform, but after calling shapesize, shapetransform then doubles in size, like it should.

Have a patch that fixes this. Rather than calling self._update() directory, we should be calling self._pen(resizemode="user"), since the user is changing the size of the turtle, just like how shapesize and shearfactor are updating.

New changeset 39b094798e14 by Raymond Hettinger in branch '3.4':
Issue #21812:  Trigger immediate transformation in turtle.shapetransform().
http://hg.python.org/cpython/rev/39b094798e14

Thanks for noticing this and for the patch.

In the future, to make patches easier to review, please isolate the core logic change from inconsequential whitespace and linewrap edits.  Also note that breaking strings in the middle to accommodate a max line length can be error-prone (in this case a space was dropped between "matrix:" and "must").

Absolutely! I totally forgot I made those changes for PEP8! Next time, I will totally submit just the change associated with the ticket.

Thank you, Raymond, for the feedback and reviewing my code!