Sage extends Python syntax by using a preparser; e.g.
sage: preparse('Zx.<x> = ZZ[]')
"Zx = ZZ['x']; (x,) = Zx._first_ngens(1)"
and so everything at Sage prompt is automatically preparsed.
I don't know whether you can force this upon PyCharm,
but you can still use everything you need using Python syntax.
Note that the Sage library is written this way (no preparser),
so there are plenty of examples there;
also e.g. your example would be just
import sage.all
from sage.all import ZZ
Zx = ZZ['x']
(x,) = Zx._first_ngens(1)
# or just (x,)=Zx.gens()