Main.py json response error

After running main.py I get an error:

[pawel@phantom ~]$ python3 main.py
Current position: {"x": 0, "y": 0, "z": 0}
Homing
Traceback (most recent call last):
  File "main.py", line 64, in <module>
    values = [a for a in values if a >= 0 ]
  File "main.py", line 64, in <listcomp>
    values = [a for a in values if a >= 0 ]
TypeError: '>=' not supported between instances of 'str' and 'int'
[pawel@phantom ~]$

I assume that problem lies in stage.py code. It looks like function doesn't return value.

pawel1010 / Openflexure-confocal-microscope

Main.py json response error #3