Adds compatibility `raise_with_traceback` method to support different `raise` syntax

Unfortunately the Python 2 `raise` syntax is not supported in Python 3.3 and not all 3.4.x versions so we deal with that by using conditional imports and a compatibility layer.

readability/compat/__init__.py

@@ -0,0 +1,6 @@
+"""
+This module contains compatibility helpers for Python 2/3 interoperability.
+
+It mainly exists because their are certain incompatibilities in the Python
+syntax that can only be solved by conditionally importing different functions.
+"""

readability/compat/three.py

@@ -0,0 +1,6 @@
+def raise_with_traceback(exc_type, traceback, *args, **kwargs):
+    """
+    Raise a new exception of type `exc_type` with an existing `traceback`. All
+    additional (keyword-)arguments are forwarded to `exc_type`
+    """
+    raise exc_type(*args, **kwargs).with_traceback(traceback)

readability/compat/two.py

@@ -0,0 +1,6 @@
+def raise_with_traceback(exc_type, traceback, *args, **kwargs):
+    """
+    Raise a new exception of type `exc_type` with an existing `traceback`. All
+    additional (keyword-)arguments are forwarded to `exc_type`
+    """
+    raise exc_type(*args, **kwargs), None, traceback

readability/readability.py

@@ -202,17 +202,10 @@ class Document:
         except Exception as e:
             log.exception('error getting summary: ')
             if sys.version_info[0] == 2:
-                # This is the only reason why we can't support Python 3.3:
-                # 3.3s parser fails to accept the old syntax (although this
-                # code never runs) which would require write this line as:
-                # write this line as
-                #    Unparseable(str(e))
-                # but then we lose the traceback information. 3.4 on the
-                # other hand accepts the old syntax and would only complain
-                # at runtime.
-                raise Unparseable(str(e)), None, sys.exc_info()[2]
+                from .compat.two import raise_with_traceback
             else:
-                raise Unparseable(str(e)).with_traceback(sys.exc_info()[2])
+                from .compat.three import raise_with_traceback
+            raise_with_traceback(Unparseable, sys.exc_info()[2], str(e))
 
     def get_article(self, candidates, best_candidate, html_partial=False):
         # Now that we have the top candidate, look through its siblings for

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = py26, py27, py34
+envlist = py26, py27, py33, py34
 
 [testenv]
 deps=pytest
@@ -14,7 +14,7 @@ deps=pytest
 # requires a Compiler and the build dependencies), you can download
 # it from http://www.lfd.uci.edu/~gohlke/pythonlibs/#lxml and install it via
 # $PYTHONDIR\Scripts\pip.exe install *.whl
-#sitepackages=True
+sitepackages=True
 commands =
     pip install -r requirements.txt
     py.test