I run launchd and I get an error that says "invalid property list"
Your plist is missing at least the line &lt;true/&gt; (or &lt;false/&gt;) after the line &lt;key&gt;RunAtLoad&lt;/key&gt;.

The line &lt;string&gt;/Applications/Python 3.6&lt;/string&gt; is useless because this is just a folder but no app/binary. Your Python script may work nevertheless, provided the shebang is set properly.