Ros 2 import tf2 Python

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Hello,

I started having a look at Ros 2 (crystal) two weeks ago and really had a hard time creating a package that produces some executables. As I managed to do that I tried to migrate some old code to Ros 2 code. It was just a tiny project which moved a frame in a circel around the world-frame's center in rviz. To do that I used the TransformBroadcaster imported from tf. I saw that there is now tf2 in my rosdistro/share, so I tried to import that with import tf2, but this threw a

ModuleNotFoundError: No module named 'tf2'

The weird thing is, I can import TFMessage from tf2_msgs and publish TFMessages to tf 'by hand'. This really feels like I overlooked something trivial but as I didn't find anything so far I wanted to ask here.