py3 compatibility for converters

rtools/helpers/converters.py

@@ -21,14 +21,22 @@ codes, e.h. ase2rdkit or ase2pybel.
 Author: Christoph Schober, 2015
 
 """
-import StringIO
+
+try:
+        import StringIO as io
+except ImportError:
+        import io
+
 import ase
 import ase.io
 
 try:
     import pybel as pb
 except ImportError:
-    print('pybel is not installed, related methods will fail.')
+    try:
+        import openbabel.pybel as pb
+    except:
+        print('pybel is not installed, related methods will fail.')
 
 try:
     from rdkit import Chem
@@ -107,7 +115,7 @@ def xyz2ase(xyz_str):
     """
     Convert a xyz file to an ASE atoms object via in-memory file (StringIO).
     """
-    xyzfile = StringIO.StringIO()
+    xyzfile = io.StringIO()
     xyzfile.write(xyz_str)
     mol = ase.io.read(xyzfile, format="xyz")
     return mol