pickle for Function and Derivative

[Thomas Ligon]

Should pickle work for Function and Derivative? I found Sympy issue #4297 and the answer seems to be no.
Nevertheless, here is what I have:
I have a private dictionary containing expressions of symbols, and everything works fine.
Then I created a new private dictionary that includes Function and Derivative, and I can't pickle it. Here are some code snippets:

    q1S, q2S = symbols('q1, q2')
    q1F = Function('q1')
...
    varX = globals()['CuspData']
    fileName = os.path.join(config.pickle_dir, 'CuspData.pckl')
    f = open(fileName, "wb")
    varX = {'q1d0': q1F(tS), 'q1d1': Derivative(q1F(tS), tS)} # test
    #with evaluate(False): pickle.dump(varX, f)
    pickle.dump(varX, f)
    f.close()
The error is "Can't pickle q1: attribute lookup q1 on __main__ failed"

[Carl K]

I've had good luck with CloudPickle, a package, when Pickle doesn't work.

---

From: sy...@googlegroups.com <sy...@googlegroups.com> on behalf of Thomas Ligon <thomas...@gmail.com>
Sent: Saturday, January 28, 2023 8:38:46 AM
To: sympy <sy...@googlegroups.com>
Subject: [sympy] pickle for Function and Derivative

 

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[Oscar Benjamin]

You need to call the variable the same name as the function:

q1 = Function('q1')

--
Oscar

[Thomas Ligon]

Thanks! That was easy and works fine.