Fix problems with side effects and python 2.6.

The isolation decorator wasn't working correctly (side effects were leaking
into other tests by breaking the user namespace).  Rewrote it to instead use a
simpler but more robust strategy (that is also faster).  See detailed comment
in source for more.

I discovered that some tests were failing when running with python 2.6 because
of changes in the behavior of int and the new print-as-a-function that Wx seems
to activate.  Updated the code to cope with both 2.5 and 2.6.

IPython/frontend/tests/test_prefilterfrontend.py

@@ -15,6 +15,7 b' __docformat__ = "restructuredtext en"'
 from copy import copy, deepcopy
 from cStringIO import StringIO
 import string
+import sys
 
 from nose.tools import assert_equal
 
@@ -23,22 +24,6 b' from IPython.ipapi import get as get_ipython0'
 from IPython.testing.plugin.ipdoctest import default_argv
 
 
-def safe_deepcopy(d):
-    """ Deep copy every key of the given dict, when possible. Elsewhere
-        do a copy.
-    """
-    copied_d = dict()
-    for key, value in d.iteritems():
-        try:
-            copied_d[key] = deepcopy(value)
-        except:
-            try:
-                copied_d[key] = copy(value)
-            except:
-                copied_d[key] = value
-    return copied_d
-
-
 class TestPrefilterFrontEnd(PrefilterFrontEnd):
     
     input_prompt_template = string.Template('')
@@ -72,17 +57,34 b' def isolate_ipython0(func):'
         with arguments.
     """
     def my_func():
-        iplib = get_ipython0()
-        if iplib is None:
+        ip0 = get_ipython0()
+        if ip0 is None:
             return func()
-        ipython0 = iplib.IP
-        global_ns = safe_deepcopy(ipython0.user_global_ns)
-        user_ns = safe_deepcopy(ipython0.user_ns)
+        # We have a real ipython running...
+        user_ns = ip0.IP.user_ns
+        user_global_ns = ip0.IP.user_global_ns
+
+        # Previously the isolation was attempted with a deep copy of the user
+        # dicts, but we found cases where this didn't work correctly. I'm not
+        # quite sure why, but basically it did damage the user namespace, such
+        # that later tests stopped working correctly.  Instead we use a simpler
+        # approach, just computing the list of added keys to the namespace and
+        # eliminating those afterwards.  Existing keys that may have been
+        # modified remain modified.  So far this has proven to be robust.
+
+        # Compute set of old local/global keys
+        old_locals = set(user_ns.keys())
+        old_globals = set(user_global_ns.keys())
         try:
             out = func()
         finally:
-            ipython0.user_ns = user_ns
-            ipython0.user_global_ns = global_ns
+            # Find new keys, and if any, remove them
+            new_locals = set(user_ns.keys()) - old_locals
+            new_globals = set(user_global_ns.keys()) - old_globals
+            for k in new_locals:
+                del user_ns[k]
+            for k in new_globals:
+                del user_global_ns[k]
         # Undo the hack at creation of PrefilterFrontEnd
         from IPython import iplib
         iplib.InteractiveShell.isthreaded = False
@@ -97,7 +99,7 b' def test_execution():'
     """ Test execution of a command.
     """
     f = TestPrefilterFrontEnd()
-    f.input_buffer = 'print 1'
+    f.input_buffer = 'print(1)'
     f._on_enter()
     out_value = f.out.getvalue()
     assert_equal(out_value, '1\n')
@@ -228,7 +230,14 b' def test_completion_indexing():'
     f._on_enter()
     f.input_buffer = 'a[0].'
     f.complete_current_input()
-    assert_equal(f.input_buffer, 'a[0].__')
+
+    if sys.version_info[:2] >= (2,6):
+        # In Python 2.6, ints picked up a few non __ methods, so now there are
+        # no completions.
+        assert_equal(f.input_buffer, 'a[0].')
+    else:
+        # Right answer for 2.4/2.5
+        assert_equal(f.input_buffer, 'a[0].__')
 
 
 @isolate_ipython0
@@ -238,8 +247,13 b' def test_completion_equal():'
     f = TestPrefilterFrontEnd()
     f.input_buffer = 'a=1.'
     f.complete_current_input()
-    assert_equal(f.input_buffer, 'a=1.__')
-
+    if sys.version_info[:2] >= (2,6):
+        # In Python 2.6, ints picked up a few non __ methods, so now there are
+        # no completions.
+        assert_equal(f.input_buffer, 'a=1.')
+    else:
+        # Right answer for 2.4/2.5
+        assert_equal(f.input_buffer, 'a=1.__')
 
 
 if __name__ == '__main__':