Fix issue #63: Use the PEP302 meta path hook to import six.moves.

Now six imports the synthetic package six.moves and its submodules on demand.
This avoids problems with code, that scans the content of sys.modules.

1 files changed, 98 insertions, 35 deletions

diff --git a/six.py b/six.py
index 019130f..82825f0 100644
--- a/six.py
+++ b/six.py
@@ -83,11 +83,7 @@ class _LazyDescr(object):
         self.name = name
 
     def __get__(self, obj, tp):
-        try:
-            result = self._resolve()
-        except ImportError:
-            # See the nice big comment in MovedModule.__getattr__.
-            raise AttributeError("%s could not be imported " % self.name)
+        result = self._resolve()
         setattr(obj, self.name, result) # Invokes __set__.
         # This is a bit ugly, but it avoids running this again.
         delattr(obj.__class__, self.name)
@@ -109,22 +105,7 @@ class MovedModule(_LazyDescr):
         return _import_module(self.mod)
 
     def __getattr__(self, attr):
-        # It turns out many Python frameworks like to traverse sys.modules and
-        # try to load various attributes. This causes problems if this is a
-        # platform-specific module on the wrong platform, like _winreg on
-        # Unixes. Therefore, we silently pretend unimportable modules do not
-        # have any attributes. See issues #51, #53, #56, and #63 for the full
-        # tales of woe.
-        #
-        # First, if possible, avoid loading the module just to look at __file__,
-        # __name__, or __path__.
-        if (attr in ("__file__", "__name__", "__path__") and
-            self.mod not in sys.modules):
-            raise AttributeError(attr)
-        try:
-            _module = self._resolve()
-        except ImportError:
-            raise AttributeError(attr)
+        _module = self._resolve()
         value = getattr(_module, attr)
         setattr(self, attr, value)
         return value
@@ -170,9 +151,72 @@ class MovedAttribute(_LazyDescr):
         return getattr(module, self.attr)
 
 
+class _SixMetaPathImporter(object):
+    """
+    A meta path importer to import six.moves and its submodules.
+
+    This class implements a PEP302 finder and loader. It should be compatible
+    with Python 2.5 and all existing versions of Python3
+    """
+    def __init__(self, six_module_name):
+        self.name = six_module_name
+        self.known_modules = {}
+
+    def _add_module(self, mod, *fullnames):
+        for fullname in fullnames:
+            self.known_modules[self.name + "." + fullname] = mod
+
+    def _get_module(self, fullname):
+        return self.known_modules[self.name + "." + fullname]
+
+    def find_module(self, fullname, path=None):
+        if fullname in self.known_modules:
+            return self
+        return None
+
+    def __get_module(self, fullname):
+        try:
+            return self.known_modules[fullname]
+        except KeyError:
+            raise ImportError("This loader does not know module " + fullname)
+
+    def load_module(self, fullname):
+        try:
+            # in case of a reload
+            return sys.modules[fullname]
+        except KeyError:
+            pass
+        mod = self.__get_module(fullname)
+        if isinstance(mod, MovedModule):
+            mod = mod._resolve()
+        else:
+            mod.__loader__ = self
+        sys.modules[fullname] = mod
+        return mod
+
+    def is_package(self, fullname):
+        """
+        Return true, if the named module is a package.
+
+        We need this method to get correct spec objects with
+        Python 3.4 (see PEP451)
+        """
+        return hasattr(self.__get_module(fullname), "__path__")
+
+    def get_code(self, fullname):
+        """Return None
+
+        Required, if is_package is implemented"""
+        self.__get_module(fullname)  # eventually raises ImportError
+        return None
+    get_source = get_code  # same as get_code
+
+_importer = _SixMetaPathImporter(__name__)
+
 
 class _MovedItems(_LazyModule):
     """Lazy loading of moved objects"""
+    __path__ = []  # mark as package
 
 
 _moved_attributes = [
@@ -239,12 +283,13 @@ _moved_attributes = [
 for attr in _moved_attributes:
     setattr(_MovedItems, attr.name, attr)
     if isinstance(attr, MovedModule):
-        sys.modules[__name__ + ".moves." + attr.name] = attr
+        _importer._add_module(attr, "moves." + attr.name)
 del attr
 
 _MovedItems._moved_attributes = _moved_attributes
 
-moves = sys.modules[__name__ + ".moves"] = _MovedItems(__name__ + ".moves")
+moves = _MovedItems(__name__ + ".moves")
+_importer._add_module(moves, "moves")
 
 
 class Module_six_moves_urllib_parse(_LazyModule):
@@ -275,7 +320,8 @@ del attr
 
 Module_six_moves_urllib_parse._moved_attributes = _urllib_parse_moved_attributes
 
-sys.modules[__name__ + ".moves.urllib_parse"] = sys.modules[__name__ + ".moves.urllib.parse"] = Module_six_moves_urllib_parse(__name__ + ".moves.urllib_parse")
+_importer._add_module(Module_six_moves_urllib_parse(__name__ + ".moves.urllib_parse"),
+                      "moves.urllib_parse", "moves.urllib.parse")
 
 
 class Module_six_moves_urllib_error(_LazyModule):
@@ -293,7 +339,8 @@ del attr
 
 Module_six_moves_urllib_error._moved_attributes = _urllib_error_moved_attributes
 
-sys.modules[__name__ + ".moves.urllib_error"] = sys.modules[__name__ + ".moves.urllib.error"] = Module_six_moves_urllib_error(__name__ + ".moves.urllib.error")
+_importer._add_module(Module_six_moves_urllib_error(__name__ + ".moves.urllib.error"),
+                      "moves.urllib_error", "moves.urllib.error")
 
 
 class Module_six_moves_urllib_request(_LazyModule):
@@ -341,7 +388,8 @@ del attr
 
 Module_six_moves_urllib_request._moved_attributes = _urllib_request_moved_attributes
 
-sys.modules[__name__ + ".moves.urllib_request"] = sys.modules[__name__ + ".moves.urllib.request"] = Module_six_moves_urllib_request(__name__ + ".moves.urllib.request")
+_importer._add_module(Module_six_moves_urllib_request(__name__ + ".moves.urllib.request"),
+                      "moves.urllib_request", "moves.urllib.request")
 
 
 class Module_six_moves_urllib_response(_LazyModule):
@@ -360,7 +408,8 @@ del attr
 
 Module_six_moves_urllib_response._moved_attributes = _urllib_response_moved_attributes
 
-sys.modules[__name__ + ".moves.urllib_response"] = sys.modules[__name__ + ".moves.urllib.response"] = Module_six_moves_urllib_response(__name__ + ".moves.urllib.response")
+_importer._add_module(Module_six_moves_urllib_response(__name__ + ".moves.urllib.response"),
+                      "moves.urllib_response", "moves.urllib.response")
 
 
 class Module_six_moves_urllib_robotparser(_LazyModule):
@@ -376,22 +425,24 @@ del attr
 
 Module_six_moves_urllib_robotparser._moved_attributes = _urllib_robotparser_moved_attributes
 
-sys.modules[__name__ + ".moves.urllib_robotparser"] = sys.modules[__name__ + ".moves.urllib.robotparser"] = Module_six_moves_urllib_robotparser(__name__ + ".moves.urllib.robotparser")
+_importer._add_module(Module_six_moves_urllib_robotparser(__name__ + ".moves.urllib.robotparser"),
+                      "moves.urllib_robotparser", "moves.urllib.robotparser")
 
 
 class Module_six_moves_urllib(types.ModuleType):
     """Create a six.moves.urllib namespace that resembles the Python 3 namespace"""
-    parse = sys.modules[__name__ + ".moves.urllib_parse"]
-    error = sys.modules[__name__ + ".moves.urllib_error"]
-    request = sys.modules[__name__ + ".moves.urllib_request"]
-    response = sys.modules[__name__ + ".moves.urllib_response"]
-    robotparser = sys.modules[__name__ + ".moves.urllib_robotparser"]
+    __path__ = []  # mark as package
+    parse = _importer._get_module("moves.urllib_parse")
+    error = _importer._get_module("moves.urllib_error")
+    request = _importer._get_module("moves.urllib_request")
+    response = _importer._get_module("moves.urllib_response")
+    robotparser = _importer._get_module("moves.urllib_robotparser")
 
     def __dir__(self):
         return ['parse', 'error', 'request', 'response', 'robotparser']
 
-
-sys.modules[__name__ + ".moves.urllib"] = Module_six_moves_urllib(__name__ + ".moves.urllib")
+_importer._add_module(Module_six_moves_urllib(__name__ + ".moves.urllib"),
+                      "moves.urllib")
 
 
 def add_move(move):
@@ -644,3 +695,15 @@ def add_metaclass(metaclass):
                 orig_vars.pop(slots_var)
         return metaclass(cls.__name__, cls.__bases__, orig_vars)
     return wrapper
+
+# Complete the moves implementation.
+# This code is at the end of this module to speed up module loading.
+# 1. turn this module into a package.
+__path__ = []  # required for PEP 302 and PEP 451
+__package__ = __name__  # see PEP 366 @ReservedAssignment
+try:
+    __spec__.submodule_search_locations = []  # PEP 451 @UndefinedVariable
+except NameError:
+    pass
+# 2. add the importer to the meta path import hook.
+sys.meta_path.append(_importer)