add tests for using python invoke and python style variables

unittest/python/func.py

@@ -0,0 +1,18 @@
+
+from __future__ import print_function
+
+def square(val):
+    return val*val
+
+def printnum():
+    print("2.25")
+
+def printtxt():
+    print("sometext")
+
+def getidxvar(lmpptr):
+    from lammps import lammps, LMP_VAR_EQUAL
+    lmp = lammps(ptr=lmpptr)
+
+    val = lmp.extract_variable("idx",None,LMP_VAR_EQUAL)
+    print(val)