Add standalone serialization function

This commit adds a standalone serialization function to the symengine
wrapper module. Previously there was a load_basic() function that could
be used for directly deserializing the payload without going through
pickle, but no corresponding function for serialization. A new function
save_basic() is added here to perform this function which will enable
users to directly roundtrip symengine objects through binary
serialization.

Fixes symengine#449

symengine/lib/symengine_wrapper.in.pyx

@@ -833,6 +833,9 @@ cdef list vec_pair_to_list(symengine.vec_pair& vec):
 def load_basic(bytes s):
     return c2py(symengine.wrapper_loads(s))
 
+def save_basic(Basic basic):
+    return symengine.wrapper_dumps(basic)
+
 
 repr_latex=[False]
 

symengine/tests/test_pickling.py

@@ -1,4 +1,5 @@
 from symengine import symbols, sin, sinh, have_numpy, have_llvm, cos, Symbol
+from symengine.lib.symengine_wrapper import load_basic, save_basic
 from symengine.test_utilities import raises
 import pickle
 import unittest
@@ -11,6 +12,12 @@ def test_basic():
     expr2 = pickle.loads(s)
     assert expr == expr2
 
+def test_basic_direct():
+    x, y, z = symbols('x y z')
+    expr = sin(cos(x + y)/z)**2
+    s = save_basic(expr)
+    expr2 = load_basic(s)
+    assert expr == expr2
 
 class MySymbolBase(Symbol):
     def __init__(self, name, attr):