I'm trying to run Appium tests written in python 3 on AWS Device Farm.
As stated in the [documentation](https://docs.aws.amazon.com/devicefarm/latest/developerguide/test-types-appium.html),

> 
> Python 2.7 is supported in both the standard environment and using Custom Mode. It is the default in both when specifying Python.  
>   
> 
> Python 3 is only supported in Custom Mode. To choose Python 3 as your python version, change the test spec to set the PYTHON\_VERSION to 3, as shown here:  
> 
> 
> 
> 

```
phases:
  install:
    commands:
      # ...
      - export PYTHON_VERSION=3
      - export APPIUM_VERSION=1.14.2
      # Activate the Virtual Environment that Device Farm sets up for Python 3, then use Pip to install required packages.
      - cd $DEVICEFARM_TEST_PACKAGE_PATH
      - . bin/activate
      - pip install -r requirements.txt
      # ...

```

I did run tests successfully on Device Farm in the past, using a python 3 custom environment, with this spec file (I include the install phase only):

```
phases:
  install:
    commands:
      # Device Farm support two major versions of Python, each with one minor version: 2 (minor version 2.7), and 3 (minor version 3.7.4).
      # The default Python version is 2, but you can switch to 3 by setting the following variable to 3:
      - export PYTHON_VERSION=3

      # This command will install your dependencies and verify that they're using the proper versions that you specified in your requirements.txt file. Because Device Farm preconfigures your environment within a
      # Python Virtual Environment in its setup phase, you can use pip to install any Python packages just as you would locally.
      - cd $DEVICEFARM_TEST_PACKAGE_PATH
      - . bin/activate
      - pip install -r requirements.txt
  # ...

```

Now, when I run the tests, I get this log an then the test crashes due to incompatible code.

```
[DEVICEFARM] ########### Entering phase test ###########

[DeviceFarm] echo "Navigate to test package directory"
Navigate to test package directory
[DeviceFarm] cd $DEVICEFARM_TEST_PACKAGE_PATH
[DeviceFarm] echo "Start Appium Python test"
Start Appium Python test
[DeviceFarm] py.test tests/ --junit-xml $DEVICEFARM_LOG_DIR/junitreport.xml
============================= test session starts ==============================
platform linux2 -- Python 2.7.6, pytest-2.8.5, py-1.4.31, pluggy-0.3.1
rootdir: /tmp/scratchrPuGRa.scratch/test-packageM5E89M/tests, inifile: 
collected 0 items / 3 errors

==================================== ERRORS ====================================
____________________ ERROR collecting test_home_buttons.py _____________________
/usr/local/lib/python2.7/dist-packages/_pytest/python.py:610: in _importtestmodule
    mod = self.fspath.pyimport(ensuresyspath=importmode)

```

Is python 3.x not supported anymore, or have there been undocumented changes?
Is there a new way to run tests in a python 3 environment?