[Python] Why Does Sympy Say This Derivative Is Constant When It's Obviously Not?

I am trying to make a Jacobian matrix using sympy.

I want to make a matrix of 2nd order derivatives, which I will call a 2nd order Jacobian.

I did this:

gk_letters = ["Δ", "Γ", "v"]

def greek_symbols():
return symbols(" ".join(gk_letters))

def partials_1st_order():
rows = []
gks = greek_symbols()
for idx1 in range(len(gk_letters)):
gk1 = gks[idx1]
col = []
for idx2 in range(len(gk_letters)):
gk2 = gks[idx2]
if gk1 == gk2:
col.append(1)
else:
col.append(Derivative(gk1, gk2))
rows.append(col)
return gks, Matrix(rows)

def partials_2nd_order():
gks, jacobian = partials_1st_order()
y = zeros(len(gks)**2, len(gks))
input_rows, input_cols = jacobian.shape
output_chunk = 0
for den_idx in range(len(gks)):
denominator = gks[den_idx]
for input_row_num in range(input_rows):
for input_col_num in range(input_cols):
numerator = jacobian[input_row_num, input_col_num]
new_diff = Derivative(numerator, denominator)
y[output_chunk*len(gks) + input_row_num, input_col_num] = new_diff
output_chunk += 1
return y



When I call partials_2nd_order() at the command prompt, I get this:

⎡ 2 2 ⎤
⎢ d d d ⎥
⎢ ──(1) ─────(Δ) ─────(Δ)⎥
⎢ dΔ dΔ dΓ dΔ dv ⎥
⎢ ⎥
⎢ 2 2 ⎥
⎢ d d d ⎥
⎢ ───(Γ) ──(1) ─────(Γ)⎥
⎢ 2 dΔ dΔ dv ⎥
⎢ dΔ ⎥
⎢ ⎥
...
⎢ ⎥
⎢ 2 2 ⎥
⎢ d d d ⎥
⎢─────(v) ─────(v) ──(1) ⎥
⎣dv dΔ dv dΓ dv ⎦


I want to collapse to 0 everything that will always be 0, such as derivatives of constants.

However, when I try this:

[jj.is_constant() for jj in x]


I get this:

[True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True]


In other words, sympy thinks everything in this matrix is constant.

What am I missing?

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