[Python] SymPy lambdify throws NameError due to Subs in derivative expression

I want to use sympy.lambdify to compute the derivative of various formulas and evaluate them numerically. Here’s a minimal example:

import sympy as sp
from sympy.utilities.lambdify import lambdify

formula = "arcsin(a**x)"
formula = sp.sympify(formula.strip(), evaluate=False)
d_formula = sp.diff(formula, "x", simplify=False)
grad_func = lambdify(["a","x"], d_formula, modules='numpy')
res = grad_func(0.5,2)


However, when I run this, I get the following error:

---------------------------------------------------------------------------
NameError Traceback (most recent call last)
Cell In[72], line 5
3 d_formula = sp.diff(formula, "x", simplify=False)
4 grad_func = lambdify(["a","x"], d_formula, modules='numpy')
----> 5 grad_func(0.5,2)

File <lambdifygenerated-938>:4, in _lambdifygenerated(a, x)
1 def _lambdifygenerated(a, x):
2 return ( # Not supported in Python with numpy:
3 # Derivative
----> 4 a**x*log(a)*Subs(Derivative(arcsin(_xi_1), _xi_1), xi_1_7206919208181693502, a**x))

NameError: name 'Subs' is not defined


I use .doit() to force evaluation of Subs, but it doesn’t seem to work. I also change the differentiation options like simplify=False, but it has no effect.

Why does sympy.diff() introduce a Subs expression here and how to avoid it？ How can I transform this derivative into a form that lambdify can handle without errors?

Any insights or alternative approaches would be greatly appreciated!

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