__reduce__ for PyPtxt (#248)

* added __reduce__ to  PyPtxt.pyx

* updated Demo_4_SaveNRestore.py

---------

Co-authored-by: Tanish Malekar <tanish.malekar@bfhl.in>

Pyfhel/PyPtxt.pyx

@@ -151,6 +151,17 @@ cdef class PyPtxt:
     # =========================================================================
     # ================================== I/O ==================================
     # =========================================================================
+    def __reduce__(self):
+        """__reduce__()
+
+        Required for pickling purposes. Returns a tuple with:
+            - A callable object that will be called to create the initial version of the object.
+            - A tuple of arguments for the callable object.
+        """
+        return (PyPtxt, (None, self._pyfhel, None, self.to_bytes(), self.scheme.name))
+
+
+
     cpdef void save(self, str fileName, str compr_mode="zstd"):
         """save(str fileName)
         
@@ -311,4 +322,4 @@ cdef class PyPtxt:
         Args:
             scale (double): new scale of the ciphertext.
         """
-        (<AfsealPtxt*>(self._ptr_ptxt)).set_scale(new_scale)
+        (<AfsealPtxt*>(self._ptr_ptxt)).set_scale(new_scale)

examples/Demo_4_SaveNRestore.py

@@ -152,16 +152,20 @@
 import pickle
 pkls_pyfhel = pickle.dumps(HE)   # pickle.dump(HE, file) to dump in a file
 pkls_ctxt   = pickle.dumps(c)
+pkls_ptxt   = pickle.dumps(p) 
 
-print("5a. Pickling Pyfhel & PyCtxt objects.")
+print("5a. Pickling Pyfhel, PyCtxt & PyPtxt objects.")
 print(f"  - pkls_pyfhel: {pkls_pyfhel[:10]}...")
 print(f"  - pkls_ctxt: {pkls_ctxt[:10]}...")
+print(f"  - pkls_ptxt: {pkls_ptxt[:10]}...")
 
 # To load the objects, just call `pickle.loads`
 HE_pkl = pickle.loads(pkls_pyfhel) # pickle.load(file) to load from file
 c_pkl = pickle.loads(pkls_ctxt)
+p_pkl = pickle.loads(pkls_ptxt)
 print("5b. Loaded pickled objects")
 print(f"   - HE_pkl: {HE_pkl}")
 print(f"   - c_pkl: {c_pkl}")
+print(f"   - p_pkl: {p_pkl}")
 
 # sphinx_gallery_thumbnail_path = 'static/thumbnails/saveRestore.png'