Replace exec/eval with proper __import__.

Unfortunately for some very weird reason, this code can't be called as
a function, so I inlined a verbatim copy of importstring.import_item.

IPython/frontend.py

@@ -1,51 +1,77 b''
 """
 Shim to maintain backwards compatibility with old frontend imports.
 
 We have moved all contents of the old `frontend` subpackage into top-level
 subpackages (`html`, `qt` and `terminal`).  This will let code that was making
 `from IPython.frontend...` calls continue working, though a warning will be
 printed.
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (c) 2013, IPython Development Team.
 #
 #  Distributed under the terms of the Modified BSD License.
 #
 #  The full license is in the file COPYING.txt, distributed with this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 from __future__ import print_function
+
+# Stdlib
 import sys
 import types
 
+m = """\
+*** WARNING*** : The top-level `frontend` package has been deprecated.
+All its subpackages have been moved to the top `IPython` level."""
+
+print(m, file=sys.stderr)
+
+# FIXME: turn this into a Warning once we've fixed all our own imports.
+#raise DeprecationWarning(m)
+
 #-----------------------------------------------------------------------------
 # Class declarations
 #-----------------------------------------------------------------------------
 
 class ShimModule(types.ModuleType):
 
     def __getattribute__(self, key):
-        m = ("*** WARNING*** : The top-level `frontend` module has been deprecated.\n"
-        "Please import %s directly from the `IPython` level." % key)
-
-        # FIXME: I don't understand why, but if the print statement below is
-        # redirected to stderr, this shim module stops working.  It seems the
-        # Python import machinery has problem with redirected prints happening
-        # during the import process.  If we can't figure out a solution, we may
-        # need to leave it to print to default stdout.
-        print(m)
-        
-        # FIXME: this seems to work fine, but we should replace it with an
-        # __import__ call instead of using exec/eval.
-        exec 'from IPython import %s' % key
-        return eval(key)
+        # Use the equivalent of import_item(name), see below
+        name = 'IPython.' + key
+
+        # NOTE: the code below is copied *verbatim* from
+        # importstring.import_item. For some very strange reason that makes no
+        # sense to me, if we call it *as a function*, it doesn't work.  This
+        # has something to do with the deep bowels of the import machinery and
+        # I couldn't find a way to make the code work as a standard function
+        # call.  But at least since it's an unmodified copy of import_item,
+        # which is used extensively and has a test suite, we can be reasonably
+        # confident this is OK.  If anyone finds how to call the function, all
+        # the below could be replaced simply with:
+        #
+        # from IPython.utils.importstring import import_item
+        # return import_item('IPython.' + key)
+        
+        parts = name.rsplit('.', 1)
+        if len(parts) == 2:
+            # called with 'foo.bar....'
+            package, obj = parts
+            module = __import__(package, fromlist=[obj])
+            try:
+                pak = module.__dict__[obj]
+            except KeyError:
+                raise ImportError('No module named %s' % obj)
+            return pak
+        else:
+            # called with un-dotted string
+            return __import__(parts[0])
 
 
 # Unconditionally insert the shim into sys.modules so that further import calls
 # trigger the custom attribute access above
 
 sys.modules['IPython.frontend'] = ShimModule('frontend')