extended python demo file and minor cleanup

python/test.py

-import pygin
+# pygin python bindings demo
+
+import pygin as pg
+
+FALSE = pg.troolean(0)
+TRUE = pg.troolean(1)
+UNKNOWN = pg.troolean(2)
+
+
+def check_if_zero(dist):
+    if dist.is_zero() == FALSE:
+        print("given distribution does not have zero mass")
+    elif dist.is_zero() == TRUE:
+        print("given distribution has zero mass")
+    elif dist.is_zero() == UNKNOWN:
+        print("it is unknown if given distribution has zero mass")
+
 
 if __name__ == "__main__":
-    dist = pygin.geometric("x", "1/2")
-    print(dist.E("x"))
+    geom_param = "p"
+    var = "x"
 
-    dist = pygin.Dist("1");
+    dist = pg.geometric(var, geom_param)
+    print(f"expected value of a {geom_param}-geometric distribution is {dist.E(var)}")
 
+    check_if_zero(dist)
+    check_if_zero(pg.Dist("0"))

src/Dist.h

@@ -63,16 +63,19 @@ namespace prodigy {
             _params.clear();
             _vars.clear();
         }
+
     private:
 
         static str2sym paramsAndVars();
 
     public:
+
         static bool isSymbKnown(const std::string& s);
         static bool isKnownAsVar(const std::string& s);
         static bool isKnownAsParam(const std::string& s);
-        static bool test() { return true; }
+
     private:
+
         static bool isSymbKnown(const symbol& s);
         static bool isKnownAsVar(const symbol& s);
         static bool isKnownAsParam(const symbol& s);
@@ -83,6 +86,7 @@ namespace prodigy {
          * new symbols are created for unknown names, but they are not registered
          */
         static ex parseWithKnownSymbs(const std::string& s);
+
         static void registerAllUnknownSymbsAsVars(const ex& e);
         static void registerAllUnknownSymbsAsParams(const ex& e);
         static void registerAsVar(const symbol& p);