shave off stat syscalls by rearranging imports

the hardest import method format to speed up is the "from x import y",
because I have no idea whether y is a module or not.

If y is a module, "from x import y" behaves similarly to the format
"import x.y; y = x.y", which means I can bypass some checks by doing the
import and equality separately.

If y is a function, "from x import y" is not equivalent to the above
format, and the import will trigger a ModuleNotFoundError. Unfortunately
I can't check for or propagate such errors during the default APE
startup without adding a whole bunch of checks, so I'd prefer to avoid
these kinds of imports unless absolutely necessary.

in this PR I avoid three such function imports in io.py and ntpath.py.
The fix is to import the module wholesale (which happens underneath
anyway) and then just check for the attribute - "import x; y = x.y",
essentially similar to how it would be if y was a module.

third_party/python/Lib/io.py

@@ -92,8 +92,6 @@ for klass in (StringIO, TextIOWrapper):
 del klass
 
 try:
-    from _io import _WindowsConsoleIO
-except ImportError:
+    RawIOBase.register(_io._WindowsConsoleIO)
+except AttributeError:
     pass
-else:
-    RawIOBase.register(_WindowsConsoleIO)

third_party/python/Lib/ntpath.py

@@ -20,6 +20,7 @@ devnull = 'nul'
 import os
 import sys
 import stat
+import posix
 import genericpath
 from genericpath import *
 
@@ -276,8 +277,8 @@ def lexists(path):
 # common case: drive letter roots. The alternative which uses GetVolumePathName
 # fails if the drive letter is the result of a SUBST.
 try:
-    from posix import _getvolumepathname
-except ImportError:
+    _getvolumepathname = posix._getvolumepathname
+except AttributeError:
     _getvolumepathname = None
 def ismount(path):
     """Test whether a path is a mount point (a drive root, the root of a
@@ -534,9 +535,9 @@ def _abspath_fallback(path):
 
 # Return an absolute path.
 try:
-    from posix import _getfullpathname
+    _getfullpathname = posix._getfullpathname
 
-except ImportError: # not running on Windows - mock up something sensible
+except AttributeError: # not running on Windows - mock up something sensible
     abspath = _abspath_fallback
 
 else:  # use native Windows method on Windows
@@ -664,7 +665,7 @@ try:
     # GetFinalPathNameByHandle is available starting with Windows 6.0.
     # Windows XP and non-Windows OS'es will mock _getfinalpathname.
     if sys.getwindowsversion()[:2] >= (6, 0):
-        from posix import _getfinalpathname
+        _getfinalpathname = posix._getfinalpathname
     else:
         raise ImportError
 except (AttributeError, ImportError, OSError):
@@ -681,7 +682,7 @@ try:
     # attribute to tell whether or not the path is a directory.
     # This is overkill on Windows - just pass the path to GetFileAttributes
     # and check the attribute from there.
-    from posix import _isdir as isdir
-except ImportError:
+    isdir = posix._isdir
+except AttributeError:
     # Use genericpath.isdir as imported above.
     pass

third_party/python/Python/import.c

@@ -128,11 +128,8 @@ static initentry ZipEntries[] = {
         {"encodings.utf_8", {.inside_zip = 1, .is_package = 0}},
         {"genericpath", {.inside_zip = 1, .is_package = 0}},
         {"io", {.inside_zip = 1, .is_package = 0}},
-        {"io._WindowsConsoleIO", {.inside_zip = 0, .is_package = 0}},
         {"ntpath", {.inside_zip = 1, .is_package = 0}},
         {"os", {.inside_zip = 1, .is_package = 0}},
-        {"posix._getfullpathname", {.inside_zip = 0, .is_package = 0}},
-        {"posix._isdir", {.inside_zip = 0, .is_package = 0}},
         {"posixpath", {.inside_zip = 1, .is_package = 0}},
         {"readline", {.inside_zip = 0, .is_package = 0}},
         {"site", {.inside_zip = 1, .is_package = 0}},
@@ -2811,8 +2808,9 @@ static PyObject *CosmoImporter_find_spec(PyObject *cls, PyObject **args,
   key.tab = NULL;
   res = bsearch(&key, ZipCdir_Lookup.entries, ZipCdir_Lookup.n, sizeof(initentry), cmp_initentry);
   if (res) {
-      if (!res->inside_zip)
+      if (!res->inside_zip) {
           Py_RETURN_NONE;
+      }
       inside_zip = res->inside_zip;
       is_package = res->is_package;
   }