You can launch a terminal via a command; this should include an option to execute a command inside the terminal as well.
There are various GUI terminal applications available on GNU/Linux. They are usually paired with the DE (desktop environment). The default DE on Raspbian ("the DE formerly known as PIXEL", for lack of a better name1) is derived from LXDE, whose terminal app is lxterminal. You can read the documentation for that with man lxterminal. The execute option is -e, so:
lxterminal -e "/usr/bin/python /home/pi/myscript.py"
Using quotes here is required if the command contains whitespace. Beware that the terminal will close when myscript.py ends, which can make it hard to determine what went wrong if it doesn't work properly.
To get around that what should work (I'm not an LXDE user, but I tested it with another terminal app) is to wrap it in a shell script:
#!/bin/sh
/usr/bin/python /home/pi/myscript.py
$SHELL
This will open a shell (ie., your normal command line) after myscript.py exits. So to use this, lxterminal -e "/path/to/that/script". The script must be executable (chmod a+x whatever.sh).
- Why they decided the DE should not have a name I don't know. It seems the opposite of user friendly, but perhaps that depends which way your head is on.