from sympy import symbols, Function
import sympy.functions as sym
from sympy import init_printing
from sympy import pprint
from sympy import Symbol
x = Symbol('x')
# If a cell contains only the following, it will render perfectly.
(pi + x)**2
# However I would like to control what to print in a function,
# so that multiple expressions can be printed from a single notebook cell.
pprint((pi + x)**2)
you need to use display:
from IPython.display import display display(yourobject)
It will choose the appropriate representation (text/LaTex/png...)