Speed up importing of past.translation (issue #117)

Also: give more descriptive error messages if top-level packages are imported
somehow on Py3.

Author: edschofield

src/_dummy_thread/__init__.py

@@ -5,4 +5,6 @@
 if sys.version_info[0] < 3:
     from dummy_thread import *
 else:
-    raise ImportError('Cannot import module from python-future source folder')
+    raise ImportError('This package should not be accessible on Python 3. '
+                      'Either you are trying to run from the python-future src folder '
+                      'or your installation of python-future is corrupted.')

src/_markupbase/__init__.py

@@ -5,4 +5,6 @@
 if sys.version_info[0] < 3:
     from markupbase import *
 else:
-    raise ImportError('Cannot import module from python-future source folder')
+    raise ImportError('This package should not be accessible on Python 3. '
+                      'Either you are trying to run from the python-future src folder '
+                      'or your installation of python-future is corrupted.')

src/_thread/__init__.py

@@ -5,4 +5,6 @@
 if sys.version_info[0] < 3:
     from dummy_thread import *
 else:
-    raise ImportError('Cannot import module from python-future source folder')
+    raise ImportError('This package should not be accessible on Python 3. '
+                      'Either you are trying to run from the python-future src folder '
+                      'or your installation of python-future is corrupted.')

src/builtins/__init__.py

@@ -7,4 +7,6 @@
     # Overwrite any old definitions with the equivalent future.builtins ones:
     from future.builtins import *
 else:
-    raise ImportError('Cannot import module from python-future source folder')
+    raise ImportError('This package should not be accessible on Python 3. '
+                      'Either you are trying to run from the python-future src folder '
+                      'or your installation of python-future is corrupted.')

src/configparser/__init__.py

@@ -3,5 +3,11 @@
 
 if sys.version_info[0] < 3:
     from ConfigParser import *
+    try:
+        from ConfigParser import (_Chainmap, Error, InterpolationMissingOptionError)
+    except ImportError:
+        pass
 else:
-    raise ImportError('Cannot import module from python-future source folder')
+    raise ImportError('This package should not be accessible on Python 3. '
+                      'Either you are trying to run from the python-future src folder '
+                      'or your installation of python-future is corrupted.')

src/copyreg/__init__.py

@@ -1,9 +1,9 @@
 from __future__ import absolute_import
-from future.utils import PY3
+import sys
 
-if PY3:
-    raise ImportError('Cannot import module from python-future source folder')
-    from copyreg import *
-else:
-    __future_module__ = True
+if sys.version_info[0] < 3:
     from copy_reg import *
+else:
+    raise ImportError('This package should not be accessible on Python 3. '
+                      'Either you are trying to run from the python-future src folder '
+                      'or your installation of python-future is corrupted.')

src/future/standard_library/__init__.py

@@ -267,7 +267,7 @@ def load_module(self, name):
             # New name. Look up the corresponding old (Py2) name:
             oldname = self.new_to_old[name]
             module = self._find_and_load_module(oldname)
-            module.__future_module__ = True
+            # module.__future_module__ = True
         else:
             module = self._find_and_load_module(name)
         # In any case, make it available under the requested (Py3) name
@@ -451,7 +451,7 @@ def install_aliases():
         # We look up the module in sys.modules because __import__ just returns the
         # top-level package:
         newmod = sys.modules[newmodname]
-        newmod.__future_module__ = True
+        # newmod.__future_module__ = True
 
         __import__(oldmodname)
         oldmod = sys.modules[oldmodname]

src/html/__init__.py

@@ -1,8 +1,9 @@
 from __future__ import absolute_import
 import sys
-__future_module__ = True
 
-if sys.version_info[0] == 3:
-    raise ImportError('Cannot import module from python-future source folder')
-else:
+if sys.version_info[0] < 3:
     from future.moves.html import *
+else:
+    raise ImportError('This package should not be accessible on Python 3. '
+                      'Either you are trying to run from the python-future src folder '
+                      'or your installation of python-future is corrupted.')

src/http/__init__.py

@@ -1,8 +1,9 @@
 from __future__ import absolute_import
 import sys
-__future_module__ = True
 
 if sys.version_info[0] < 3:
     pass
 else:
-    raise ImportError('Cannot import module from python-future source folder')
+    raise ImportError('This package should not be accessible on Python 3. '
+                      'Either you are trying to run from the python-future src folder '
+                      'or your installation of python-future is corrupted.')

src/http/client.py

@@ -1,8 +1,6 @@
 from __future__ import absolute_import
 import sys
-__future_module__ = True
 
-if sys.version_info[0] < 3:
-    from httplib import *
-else:
-    raise ImportError('Cannot import module from python-future source folder')
+assert sys.version_info[0] < 3
+
+from httplib import *