Avoid string formatting in log call

Remove handler and warning.warn

odo/core.py

@@ -9,7 +9,6 @@
 from .utils import expand_tuples, ignoring
 
 log = logging.getLogger(__name__)
-log.addHandler(logging.NullHandler())
 
 ooc_types = set()  # Out-of-Core types
 
@@ -58,17 +57,20 @@ def _transform(graph, target, source, excluded_edges=None, ooc_types=ooc_types,
     pth = path(graph, type(source), target,
                excluded_edges=excluded_edges,
                ooc_types=ooc_types)
+
     try:
         for (A, B, f) in pth:
-            log.debug('[{src} -> {dest}] {f} ({kwargs})'.format(f=f.__name__,
-                            kwargs=kwargs, src=A.__name__, dest=B.__name__))
+            log.debug("Transforming %s -> %s", A.__name__, B.__name__,
+                        extra={'kwargs': kwargs, 'f': f, 'excluded_edges': excluded_edges}
+            )
             x = f(x, excluded_edges=excluded_edges, **kwargs)
         return x
     except NotImplementedError as e:
         if kwargs.get('raise_on_errors'):
             raise
-        warn(FailedConversionWarning(A, B, e))
-        log.warning('Failed Conversion {} -> {} ({})'.format(A, B, str(e)))
+        log.warning('Failed on %s -> %s. Working around\nError message:\n%s', 
+            A.__name__, B.__name__, e
+        )
         new_exclusions = excluded_edges | set([(A, B)])
         return _transform(graph, target, source, excluded_edges=new_exclusions,
                           **kwargs)