oops.se
There are two different crontab one that run the "global/system" crontab and then you have a user specific crontab. And the "systems crontab" doesn't have the same environment as the "users crontab".
A workaround this is to specify the user in the systems crontab with the command, ex:
* username /path/to/your/script.py
Or you can put the script into the "users crontab" file by editing the "users crontab", ex:
sudo crontab -u username -e