how to pass expression as argument to a function without evaluating it - python-3.x

Question

First, see the relevant user code for running z3-solver. This works fine, and the solver returns some values after evaluating the expression:
# see source at https://github.com/Z3Prover/z3
# the relevant code is at: z3-master/src/api/python/z3/z3.py
# pip install z3-solver
from z3 import *
x = Int('x')
#print(type(x)) # <class 'z3.z3.ArithRef'>
y = Int('y')
s = Solver()
# print(type(s)) # <class 'z3.z3.Solver'>
s.add(x > 10) # this works
s.add(y == x + 2)
print(s)
print(s.check())
print(s.model())
Now, my short attempt at writing an evaluator like z3:
class Int():
def __init__(self,name):
self.name = name
self.value = None
def do_print(self):
print('Rand({})'.format(self.name))
def __str__(self):
return(str(self.value))
class Solver():
def add(self, *argv):
self.args = []
for arg in argv:
self.args.append(arg)
def do_print(self):
print('Constr(',end='')
for arg in self.args:
print(arg)
print(')')
x = Int('x')
s=Solver()
s.add(x > 10) # this does not work - but why is same kind of code in z3 working?
# err: TypeError: '<' not supported between instances of 'Int' and 'int'
x.do_print()
s.do_print()
I am getting an error on the s.add() line. I understand the error, that the object 'x' cannot be compared with an integer. This is happening because the expression in this line is getting evaluated before the s.add() is being called.
But my question is - how is z3-solver bypassing this error? How is it able to pass the args to add() without evaluating it first?
How do I fix the problem in my code, and pass the expression to s.add() without evaluating it first?