Merge pull request sympy#20470 from oscarbenjamin/pr_eric_17

Fix pickling of print functions (1.7 branch)

sympy/printing/printer.py

@@ -360,6 +360,12 @@ def __init__(self, f, print_cls: Type[Printer]):
         self.__print_cls = print_cls
         update_wrapper(self, f)
 
+    def __reduce__(self):
+        # Since this is used as a decorator, it replaces the original function.
+        # The default pickling will try to pickle self.__wrapped__ and fail
+        # because the wrapped function can't be retrieved by name.
+        return self.__wrapped__.__qualname__
+
     def __repr__(self) -> str:
         return repr(self.__wrapped__)  # type:ignore
 

sympy/printing/tests/test_latex.py

@@ -2702,3 +2702,8 @@ def test_global_settings():
     # check we really did undo it
     assert inspect.signature(latex).parameters['imaginary_unit'].default == 'i'
     assert latex(I) == 'i'
+
+def test_pickleable():
+    # this tests that the _PrintFunction instance is pickleable
+    import pickle
+    assert pickle.loads(pickle.dumps(latex)) is latex