phivenv/Lib/site-packages/sympy/functions/elementary/benchmarks/bench_exp.py

from sympy.core.symbol import symbols
from sympy.functions.elementary.exponential import exp

x, y = symbols('x,y')

e = exp(2*x)
q = exp(3*x)


def timeit_exp_subs():
    e.subs(q, y)