gyp: replace basestring with str, but only on Python 3.

On Python 2, basestring is (unicode, str).
On Python 3, basestring and unicode are gone, and there is only str.

gyp/pylib/gyp/MSVSSettings.py

@@ -16,6 +16,8 @@
 
 from __future__ import print_function
 
+from gyp import string_types
+
 import sys
 import re
 
@@ -108,11 +110,11 @@ class _String(_Type):
   """A setting that's just a string."""
 
   def ValidateMSVS(self, value):
-    if not isinstance(value, basestring):
+    if not isinstance(value, string_types):
       raise ValueError('expected string; got %r' % value)
 
   def ValidateMSBuild(self, value):
-    if not isinstance(value, basestring):
+    if not isinstance(value, string_types):
       raise ValueError('expected string; got %r' % value)
 
   def ConvertToMSBuild(self, value):
@@ -124,11 +126,11 @@ class _StringList(_Type):
   """A settings that's a list of strings."""
 
   def ValidateMSVS(self, value):
-    if not isinstance(value, basestring) and not isinstance(value, list):
+    if not isinstance(value, string_types) and not isinstance(value, list):
       raise ValueError('expected string list; got %r' % value)
 
   def ValidateMSBuild(self, value):
-    if not isinstance(value, basestring) and not isinstance(value, list):
+    if not isinstance(value, string_types) and not isinstance(value, list):
       raise ValueError('expected string list; got %r' % value)
 
   def ConvertToMSBuild(self, value):

gyp/pylib/gyp/__init__.py

@@ -16,6 +16,13 @@
 import traceback
 from gyp.common import GypError
 
+try:
+    # Python 2
+    string_types = basestring
+except NameError:
+    # Python 3
+    string_types = str
+
 # Default debug modes for GYP
 debug = {}
 
@@ -412,7 +419,7 @@ def gyp_main(args):
     for option, value in sorted(options.__dict__.items()):
       if option[0] == '_':
         continue
-      if isinstance(value, basestring):
+      if isinstance(value, string_types):
         DebugOutput(DEBUG_GENERAL, "  %s: '%s'", option, value)
       else:
         DebugOutput(DEBUG_GENERAL, "  %s: %s", option, value)