Add Enum and Eiffel examples using new-style classes.

1 files changed, 178 insertions, 0 deletions

diff --git a/Demo/newmetaclasses/Enum.py b/Demo/newmetaclasses/Enum.py
new file mode 100644
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+++ b/Demo/newmetaclasses/Enum.py
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+"""Enumeration metaclass."""
+
+class EnumMetaclass(type):
+    """Metaclass for enumeration.
+
+    To define your own enumeration, do something like
+
+    class Color(Enum):
+        red = 1
+        green = 2
+        blue = 3
+
+    Now, Color.red, Color.green and Color.blue behave totally
+    different: they are enumerated values, not integers.
+
+    Enumerations cannot be instantiated; however they can be
+    subclassed.
+    """
+
+    def __init__(cls, name, bases, dict):
+        super(EnumMetaclass, cls).__init__(name, bases, dict)
+        cls._members = []
+        for attr in dict.keys():
+            if not (attr.startswith('__') and attr.endswith('__')):
+                enumval = EnumInstance(name, attr, dict[attr])
+                setattr(cls, attr, enumval)
+                cls._members.append(attr)
+
+    def __getattr__(cls, name):
+        if name == "__members__":
+            return cls._members
+        raise AttributeError, name
+
+    def __repr__(cls):
+        s1 = s2 = ""
+        enumbases = [base.__name__ for base in cls.__bases__
+                     if isinstance(base, EnumMetaclass) and not base is Enum]
+        if enumbases:
+            s1 = "(%s)" % ", ".join(enumbases)
+        enumvalues = ["%s: %d" % (val, getattr(cls, val))
+                      for val in cls._members]
+        if enumvalues:
+            s2 = ": {%s}" % ", ".join(enumvalues)
+        return "%s%s%s" % (cls.__name__, s1, s2)
+
+class FullEnumMetaclass(EnumMetaclass):
+    """Metaclass for full enumerations.
+
+    A full enumeration displays all the values defined in base classes.
+    """
+
+    def __init__(cls, name, bases, dict):
+        super(FullEnumMetaclass, cls).__init__(name, bases, dict)
+        for obj in cls.__mro__:
+            if isinstance(obj, EnumMetaclass):
+                for attr in obj._members:
+                    # XXX inefficient
+                    if not attr in cls._members:
+                        cls._members.append(attr)
+
+class EnumInstance(int):
+    """Class to represent an enumeration value.
+
+    EnumInstance('Color', 'red', 12) prints as 'Color.red' and behaves
+    like the integer 12 when compared, but doesn't support arithmetic.
+
+    XXX Should it record the actual enumeration rather than just its
+    name?
+    """
+
+    def __new__(cls, classname, enumname, value):
+        return int.__new__(cls, value)
+
+    def __init__(self, classname, enumname, value):
+        self.__classname = classname
+        self.__enumname = enumname
+
+    def __repr__(self):
+        return "EnumInstance(%s, %s, %d)" % (self.__classname, self.__enumname,
+                                             self)
+
+    def __str__(self):
+        return "%s.%s" % (self.__classname, self.__enumname)
+
+class Enum:
+    __metaclass__ = EnumMetaclass
+
+class FullEnum:
+    __metaclass__ = FullEnumMetaclass
+
+def _test():
+
+    class Color(Enum):
+        red = 1
+        green = 2
+        blue = 3
+
+    print Color.red
+
+    print `Color.red`
+    print Color.red == Color.red
+    print Color.red == Color.blue
+    print Color.red == 1
+    print Color.red == 2
+
+    class ExtendedColor(Color):
+        white = 0
+        orange = 4
+        yellow = 5
+        purple = 6
+        black = 7
+
+    print ExtendedColor.orange
+    print ExtendedColor.red
+
+    print Color.red == ExtendedColor.red
+
+    class OtherColor(Enum):
+        white = 4
+        blue = 5
+
+    class MergedColor(Color, OtherColor):
+        pass
+
+    print MergedColor.red
+    print MergedColor.white
+
+    print Color
+    print ExtendedColor
+    print OtherColor
+    print MergedColor
+
+def _test2():
+
+    class Color(FullEnum):
+        red = 1
+        green = 2
+        blue = 3
+
+    print Color.red
+
+    print `Color.red`
+    print Color.red == Color.red
+    print Color.red == Color.blue
+    print Color.red == 1
+    print Color.red == 2
+
+    class ExtendedColor(Color):
+        white = 0
+        orange = 4
+        yellow = 5
+        purple = 6
+        black = 7
+
+    print ExtendedColor.orange
+    print ExtendedColor.red
+
+    print Color.red == ExtendedColor.red
+
+    class OtherColor(FullEnum):
+        white = 4
+        blue = 5
+
+    class MergedColor(Color, OtherColor):
+        pass
+
+    print MergedColor.red
+    print MergedColor.white
+
+    print Color
+    print ExtendedColor
+    print OtherColor
+    print MergedColor
+
+if __name__ == '__main__':
+    _test()
+    _test2()
+