Launch agent invoking python script returns permission error
You have one error and a minor one in your plist and probably one inconsistency in your file system:

Keeping a job alive no matter what and starting the same job every 5 minutes is like being forced to stay in the bathroom and going to the bathroom every five minutes because of ... an ablutomania.

So remove the part:

    &lt;key&gt;KeepAlive&lt;/key&gt;
    &lt;true/&gt;


Add the python bin in the program arguments:

replace:

&lt;key&gt;ProgramArguments&lt;/key&gt;
&lt;array&gt;
    &lt;string&gt;/Users/open/Library/Containers/.heheOSX/MacOSHighSierra.py&lt;/string&gt;
&lt;/array&gt;


with:

&lt;key&gt;ProgramArguments&lt;/key&gt;
&lt;array&gt;
    &lt;string&gt;/usr/bin/python&lt;/string&gt;
    &lt;string&gt;/Users/open/Library/Containers/.heheOSX/MacOSHighSierra.py&lt;/string&gt;
&lt;/array&gt;


If you prefer another python bin (e.g. some brew/python), use this one instead.

Finally make sure that the logged in user (i.e. the one launching the agent) has at least read access to /Users/open/Library/Containers/.heheOSX/MacOSHighSierra.py!



Regarding the last problem:

I use the following alias in my .bash_profile to get all permissions/ACLs of a path:

alias lspath='(IFS=/; set -f -- $PWD; for arg; do path="${path%/}/$arg"; paths+=("$path"); done; ls -dlaOe@ "${paths[@]}")'


Entering lspath after cd'ing to a folder will reveal all permissions/ACLs:

$ cd /Users/user1/Library/Containers/.heheOSX
$ lspath
drwxr-xr-x  39 root   wheel  - 1394 27 Mär 17:44 /
drwxr-xr-x   7 root   admin  -  238  5 Aug  2014 /Users
drwxr-xr-x+ 60 user1  staff  - 2040 26 Mär 23:58 /Users/user1
 0: group:everyone deny delete
drwx------+ 72 user1  staff  - 2448 16 Mär 00:40 /Users/user1/Library
 0: group:everyone deny delete
drwx------  57 user1  staff  - 1938 27 Mär 20:26 /Users/user1/Library/Containers
drwxr-xr-x   2 user1  staff  -   68 27 Mär 20:26 /Users/user1/Library/Containers/.heheOSX


In this example no other user except user1 (and root) will be able to launch/load a *.py in /Users/user1/Library/Containers/.heheOSX because other users can't traverse neither /Users/user1/Library nor /Users/user1/Library/Containers because of their restrictive drwx------ permissions.