A self-contained piece of Michael Hudson's patch

#449043 supporting __future__ in simulated shells
in support of PEP 264.

Much has changed from the patch version:
+ Repaired bad hex constant for nested_scopes.
+ Defined symbolic CO_xxx names so global search will find these uses.
+ Made the exported list of feature names explicit, instead of abusing
  __all__ for this purpose (and redefined __all__ accordingly).
+ Added gross .compiler_flag verification to test___future__.py, and
  reworked it a little to make use of the newly exported explicit list
  of feature names.

Lib/__future__.py

@@ -2,7 +2,8 @@
 
 Each line is of the form:
 
-    FeatureName = "_Feature(" OptionalRelease "," MandatoryRelease ")"
+    FeatureName = "_Feature(" OptionalRelease "," MandatoryRelease ","
+                              CompilerFlag ")"
 
 where, normally, OptionalRelease < MandatoryRelease, and both are 5-tuples
 of the same form as sys.version_info:
@@ -37,13 +38,37 @@ dropped.
 Instances of class _Feature have two corresponding methods,
 .getOptionalRelease() and .getMandatoryRelease().
 
+CompilerFlag is the (bitfield) flag that should be passed in the fourth
+argument to the builtin function compile() to enable the feature in
+dynamically compiled code.  This flag is stored in the .compiler_flag
+attribute on _Future instances.  These values must match the appropriate
+#defines of CO_xxx flags in Include/compile.h.
+
 No feature line is ever to be deleted from this file.
 """
 
+all_feature_names = [
+    "nested_scopes",
+    "generators",
+    "division",
+]
+
+__all__ = ["all_feature_names"] + all_feature_names
+
+
+# The CO_xxx symbols are defined here under the same names used by
+# compile.h, so that an editor search will find them here.  However,
+# they're not exported in __all__, because they don't really belong to
+# this module.
+CO_NESTED            = 0x0010   # nested_scopes
+CO_GENERATOR_ALLOWED = 0x1000   # generators
+CO_FUTURE_DIVISION   = 0x2000   # division
+
 class _Feature:
-    def __init__(self, optionalRelease, mandatoryRelease):
+    def __init__(self, optionalRelease, mandatoryRelease, compiler_flag):
         self.optional = optionalRelease
         self.mandatory = mandatoryRelease
+        self.compiler_flag = compiler_flag
 
     def getOptionalRelease(self):
         """Return first release in which this feature was recognized.
@@ -63,9 +88,17 @@ class _Feature:
         return self.mandatory
 
     def __repr__(self):
-        return "Feature(" + `self.getOptionalRelease()` + ", " + \
-                            `self.getMandatoryRelease()` + ")"
+        return "_Feature(" + `self.getOptionalRelease()` + ", " + \
+                             `self.getMandatoryRelease()` + ")"
 
-nested_scopes = _Feature((2, 1, 0, "beta", 1), (2, 2, 0, "alpha", 0))
-generators = _Feature((2, 2, 0, "alpha", 1), (2, 3, 0, "final", 0))
-division = _Feature((2, 2, 0, "alpha", 2), (3, 0, 0, "alpha", 0))
+nested_scopes = _Feature((2, 1, 0, "beta",  1),
+                         (2, 2, 0, "alpha", 0),
+                         CO_NESTED)
+
+generators = _Feature((2, 2, 0, "alpha", 1),
+                      (2, 3, 0, "final", 0),
+                      CO_GENERATOR_ALLOWED)
+
+division = _Feature((2, 2, 0, "alpha", 2),
+                    (3, 0, 0, "alpha", 0),
+                    CO_FUTURE_DIVISION)

Lib/test/test___future__.py

@@ -5,7 +5,7 @@ import __future__
 
 GOOD_SERIALS = ("alpha", "beta", "candidate", "final")
 
-features = [x for x in dir(__future__) if x[:1] != "_"]
+features = __future__.all_feature_names
 for feature in features:
     value = getattr(__future__, feature)
     if verbose:
@@ -39,3 +39,8 @@ for feature in features:
         verify(type(serial) is IntType, "mandatory serial isn't int")
         verify(optional < mandatory,
                "optional not less than mandatory, and mandatory not None")
+
+    verify(hasattr(value, "compiler_flag"),
+           "feature is missing a .compiler_flag attr")
+    verify(type(getattr(value, "compiler_flag")) is IntType,
+           ".compiler_flag isn't int")