Bug#896409: python-tf2-ros: tf2_ros fails to import

[Helmut Grohne]

Package: python-tf2-ros
Version: 0.5.16-2
Severity: serious
User: helmutg at debian.org
Usertags: python-import

After installing python-tf2-ros importing the module tf2_ros
into a python interpreter fails with the following error:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/tf2_ros/__init__.py", line 39, in <module>
    from buffer import *
  File "/usr/lib/python2.7/dist-packages/tf2_ros/buffer.py", line 34, in <module>
    from tf2_msgs.srv import FrameGraph, FrameGraphResponse
ImportError: No module named tf2_msgs.srv

The vast majority of import failures is attributed to missing dependencies.
Often times that manifests as an ImportError or ModuleNotFoundError.
Typically, dependencies should be inserted by dh-python via ${python:Depends}
or ${python3:Depends}. Thus a missing dependency can be caused by incomplete
install_requires in setup.py. Sometimes a missing dependency of a dependency
is the cause, in such cases this bug should be reassigned.

Helmut