context.query_devices() confuses T265

[tpwrules]

---

Required Info
Camera Model	T265
Firmware Version	0.0.18.5715
Operating System & Version	Ubuntu 18.04 LTS
Kernel Version (Linux Only)	4.15.0-50-generic
Platform	PC
SDK Version	2.22.0 (master) }
Language	Python 3.7

Issue Description

The following program displays the pose from an attached T265:

import pyrealsense2 as rs
ctx = rs.context()
print(list(ctx.query_devices()))
pipe = rs.pipeline()
pipe.start()
print(pipe.wait_for_frames().first_or_default(rs.stream.pose).as_pose_frame().get_pose_data().translation)
pipe.stop()

On the listed setup, it produces the following output when a T265 is plugged in:

$ python3 query_devices_problem.py
[<pyrealsense2.device: Intel RealSense T265 (S/N: <redacted>)>]
Traceback (most recent call last):
  File "query_devices_problem.py", line 5, in <module>
    pipe.start()
RuntimeError: No device connected

When line 2 is commented out, it produces correct output:

$ python3 query_devices_problem.py
x: -3.32125e-06, y: 0.000118504, z: -2.13213e-05

It seems that querying for devices makes the T265 inaccessible to the pipe system. This problem does not occur with a D435 (it instead crashes because the D435 does not offer pose data).

[ev-mp]

@tpwrules hello,
When working with T265 you have to share and reuse the initial context across all the pipe objects created. This limitation does not apply to other devices.

import pyrealsense2 as rs
ctx= rs.context()
print(list(ctx.query_devices()))
pipe = rs.pipeline(ctx)
pipe.start()
...

See #3734, #3697

[tpwrules]

Oh, I did not realize that I had to pass the context to the pipeline. That indeed fixes the issue.