[Tutor] Not sure how to use external command within python code (3.6)

[Robert Alexander]

I wish to use Ookla's SpeedTest CLI (https://www.speedtest.net/apps/cli ) (after trying other Python libraries I didn't like).

I'd like to issue a "speedtest -f json" command from within a python script and parse the results. 

I am currently stuck with the following code:

process = subprocess.Popen(['/usr/local/bin/speedtest', '-f json'],
                           stdout=subprocess.PIPE,
                           stderr=subprocess.PIPE)
stdout, stderr = process.communicate()
which only populates the stderr variable stating that 

[error] Invalid output format specified: json

Given on the command line that syntax is good.

What am I doing wrong?

Thank you very much

PS End goal will be monitoring the results and when they fall under a given threshold send me an email, but that's the final goal.