I define a python funciton that expects an argument that is a sympy expression. If I save it using pickle and read it back in a different session it will not load.

The error message is “Can’t Get Attribute …”, which usually means that I failed to save something that is referenced by the think I did save. I don’t know that this is the problem in this case, but it seems likely that there are some ‘global’ variables in the syppy package that need to be saved. Especially, since it works within the same session, but not across sessions.

Trouble is there is no hint about what they might be.

# This script tests pickle and for a function that uses sympy.  The test only tests within a
# single session.

import pickle
from sympy import Symbol

def SymSqr(xExp):
  return xExp * xExp

if __name__ == "__main__":
  # constants
  fileName = 'temp.pickle'
  xSym = Symbol('x')
  
  # test session defined function
  result = SymSqr(2*xSym)
  print(f'result = {result}')

  # save funciton and load it back under a different name
  with open(fileName, 'wb') as outFle:
    pickle.dump(SymSqr, outFle)

  with open(fileName, 'rb') as inFile:
    atlFunc = pickle.load(inFile)

  # test session defined function
  altResult = atlFunc(2 * xSym)
  print(f'altResult = {altResult}')

> F:Users...intra_session.py
result = 4*x**2
altResult = 4*x**2

# This script tests pickle and for a function that uses sympy.  The test reads the funciton in a 
# different session than the one in which it was saved.

import pickle
from sympy import Symbol


if __name__ == "__main__":
  # constants
  fileName = 'temp.pickle'
  xSym = Symbol('x')

  # load the functon
  with open(fileName, 'rb') as inFile:
    SymSqr = pickle.load(inFile)

  # test session defined function
  result = SymSqr(2 * xSym)
  print(f'result = {result}')

F:Users...python.exe F:Users...inter_session.py 
Traceback (most recent call last):
  File "F:Users...inter_session.py", line 15, in <module>
    SymSqr = pickle.load(inFile)
             ^^^^^^^^^^^^^^^^^^^
AttributeError: Can't get attribute 'SymSqr' on <module '__main__' from 'F:\Users\...\inter_session.py'>

Process finished with exit code 1