win: Use the _winreg module for registry access

pylib/gyp/MSVSVersion.py

Index: pylib/gyp/MSVSVersion.py
diff --git a/pylib/gyp/MSVSVersion.py b/pylib/gyp/MSVSVersion.py
index 1d836b1ec3ed6e65e71926f8320f3cc5434a48a0..22d9327ca2f9c2b93c12815651346a55dff0541e 100644
--- a/pylib/gyp/MSVSVersion.py
+++ b/pylib/gyp/MSVSVersion.py
@@ -165,8 +165,28 @@ def _RegistryQuery(key, value=None):
   return text
 
 
+def _RegistryGetValueUsingWinReg(key, value):
+  """Use the _winreg module to obtain the value of a registry key.
+
+  Args:
+    key: The registry key.
+    value: The particular registry value to read.
+  Return:
+    contents of the registry key's value, or None for failure.  Throws
+    ImportError if _winreg is unavailable.
+  """
+  import _winreg
+  try:
+    root,subkey = key.split('\\', 1)

[scottmg, 2014/11/13 18:05:35]

nit; space after ,

+    assert('HKLM' == root)  # Only need HKLM for now

[scottmg, 2014/11/13 18:05:35]

nits;
- no ()
- root == 'HKLM', rather than yoda-style
- '.' at end of comment.

+    with _winreg.OpenKey(_winreg.HKEY_LOCAL_MACHINE, subkey) as hkey:
+      return _winreg.QueryValueEx(hkey, value)[0]
+  except WindowsError:
+    return None
+
+
 def _RegistryGetValue(key, value):
-  """Use reg.exe to obtain the value of a registry key.
+  """Use _winreg or reg.exe to obtain the value of a registry key.

[scottmg, 2014/11/13 18:05:35]

add a comment explaining why we need to try both ways

 
   Args:
     key: The registry key.
@@ -174,6 +194,12 @@ def _RegistryGetValue(key, value):
   Return:
     contents of the registry key's value, or None on failure.
   """
+  try:
+    return _RegistryGetValueUsingWinReg(key, value)
+  except ImportError:
+    pass
+
+  # Fallback to reg.exe if we fail to import _winreg.
   text = _RegistryQuery(key, value)
   if not text:
     return None
@@ -184,19 +210,6 @@ def _RegistryGetValue(key, value):
   return match.group(1)
 
 
-def _RegistryKeyExists(key):
-  """Use reg.exe to see if a key exists.
-
-  Args:
-    key: The registry key to check.
-  Return:
-    True if the key exists
-  """
-  if not _RegistryQuery(key):
-    return False
-  return True
-
-
 def _CreateVersion(name, path, sdk_based=False):
   """Sets up MSVS project generation.