    """
    NamedValueAccess provides functions, a mix-in class and a wrapper class
    all for accessing Python objects by named attributes. You can use which
    ever of the three approaches best suites your needs and style.

    NOTES

    If Python provided a root class 'Object' in the same tradition as other
    OOP languages such as Smalltalk, Objective-C and Java, then we could
    dispense with the global functions and simply stick with the mix-in.

    TO DO

    * The mix-in's valueForKey() could be out of slight alignment with the
      function, since they have different implementations. However, the test
      cases pass for both right now.

    * Should the valueForKey() function provide for caching of bindings in
      the same manner than the mix-in does?
      If not, should the mix-in allow an option to *not* cache bindings?

    * hasValueForKey() function? (We already have a method in the mix-in)

    * valuesForNames() in the mix-in:
        * Change parameter 'keys' to 'names'
        * Use NoDefault instead of None in the parameters
        * Revisit doc string and test cases

    * Testing: increase coverage

    * Rename? class NamedValueAccess+ible:

    * Benchmarking: Set this up in a new file:
        Tests/BenchNamedValueAccess.py
        so we can experiment with caching vs. not and other techniques.

    PAST DESIGN DECISIONS

    * Only if a name binds to a method is it invoked. Another approach is
      to invoke any value that is __call__able, but that is unPythonic: If
      obj.foo is a class or a function then obj.foo gives that class or
      function, not the result of invoking it. Method is the only
      convenience we provide, because that's one of the major points of
      providing this.

    CREDIT

    Chuck Esterbrook <echuck@mindspring.com>
    Tavis Rudd <tavis@calrudd.com>

    """

    import types
    from MiscUtils import NoDefault

    # if technique is zero, use bound methods in the _kvGetBindings cache, otherwise use unbound
    # @@ 2000-05-31 ce: after additional testing we can probably scorge the technique=0 allowance
    technique = 1

    ## Exceptions ##

    class NamedValueAccessError(LookupError): pass
    class ValueForKeyError(NamedValueAccessError): pass

    class NamedValueAccess:
        """Mix-in class for accessing Python objects by named attributes.

        This class is intended to be ancestor class such that you can say:
            from NamedValueAccess import *
            age = someObj.valueForName("age")
            name = someObj.valueForName("info.fields.name")

        This can be useful in setups where you wish to textually refer to the
        objects in a program, such as an HTML template processed in the context
        of an object-oriented framework.

        Keys can be matched to either methods or instance variables and with
        or without underscores.

        valueForName() can also traverse bona fide dictionaries (DictType).

        You can safely import * from this module.
        Only the NamedValueAccess class is exported.

        There is no __init__() method and never will be.

        You'll see the terms 'key' and 'name' in the class and its documentation.
        A 'key' is a single identifier such as 'foo'. A name could be key, or a
        qualified key, such as 'foo.bar.boo'. Names are generally more convenient
        and powerful, while key-oriented methods are more efficient and provide
        the atomic functionality that name-oriented methods are built upon.
        From a usage point of view, you normally just use the 'name' methods
        and forget about the 'key'.

        @@ 2000-05-21 ce: This class causes problems when used in WebKit for logging.
            Perhaps circular references?
            Involving self?
            Having to do with methods bound to their objects?

        @@ 2000-03-03 ce: document instance variables

        @@ 2000-04-24 ce: Some classes like UserDict need to use getitem()
        instead of getattr() and don't need to deal with _bindingForGetKey().

        @@ 2000-05-31 ce: Rename this class to NamedValues, NamedValueAccess, ValuesByName

        @@ This class probably needs to be in MiscUtils, as it's being used in that
           way while MiddleKit was intended for "enterprise/business objects".

        """

        ## Accessing values by key ##

        def hasValueForKey(self, key):
            """Check whether key is available.

            Returns true if the key is available, although that does not guarantee
            that there will not be errors caused by retrieving the key.

            """
            return self._bindingForGetKey(key) is not None

        def valueForKey(self, key, default=NoDefault):
            """Get value for given key.

            Suppose key is 'foo'.
            This method returns the value with the following precedence:
                1. Methods before non-methods
                2. Public attributes before private attributes

            More specifically, this method then returns one of the following:
                * self.foo()
                * self._foo()
                * self.foo
                * self._foo

            ... or default, if it was specified,
            otherwise invokes and returns result of valueForUnknownKey().
            Note that valueForUnknownKey() normally returns an exception.

            See valueForName() which is a more advanced version of this method
            that allows multiple, qualified keys.

            """
            binding = self._bindingForGetKey(key)

            if not binding:
                if default is NoDefault:
                    return self.valueForUnknownKey(key, default)
                else:
                    return default

            if type(binding) is types.MethodType:
                if technique:
                    result = binding(self)
                else:
                    result = binding()
                return result
            else:
                return getattr(self, binding)

        def hasValueForName(self, keysString):
            """Check whether name is available."""
            try:
                self.valueForName(keysString)
            except NamedValueAccessError:
                return 0
            return 1

        def valueForName(self, keysString, default=None):
            """Get the value for the given keysString.

            This is the more advanced version of valueForKey(), which can only
            handle single names. This method can handle
                'foo', 'foo1.foo2', 'a.b.c.d', etc.
            It will traverse dictionaries if needed.
            """
            keys = keysString.split('.')
            return self.valueForKeySequence(keys, default)

        def valueForKeySequence(self, listOfKeys, default=None):
            """Get the value for the given list of keys."""
            return _valueForKeySequence(self, listOfKeys, default)

        def valuesForNames(self, keys, default=None, defaults=None, forgive=0, includeNames=0):
            """Get all values for given names.

            Returns a list of values that match the given keys, each of which is
            passed through valueForName() and so could be of the form 'a.b.c'.

            keys and defaults are sequences.
            default is any kind of object.
            forgive and includeNames are flags.

            If default is not None, then it is substituted when a key is not found.
            Otherwise, if defaults is not None, then its corresponding/parallel
            value for the current key is substituted when a key is not found.
            Otherwise, if forgive is true, then unknown keys simply don't produce
            any values.
            Otherwise, if default and defaults are None, and forgive is false,
            then the unknown keys will probably raise an exception through
            self.valueForUnknownKey() although that method can always return
            a final, default value.
            if keys is None, then None is returned.
            If keys is an empty list, then None is returned.
            Often these last four arguments are specified by key.
            Examples:
                names = ['origin.x', 'origin.y', 'size.width', 'size.height']
                obj.valuesForNames(names)
                obj.valuesForNames(names, default=0.0)
                obj.valuesForNames(names, defaults=[0.0, 0.0, 100.0, 100.0])
                obj.valuesForNames(names, forgive=0)
            @@ 2000-03-04 ce: includeNames is only supported when forgive=1.
                It should be supported for the other cases.
                It should be documented.
                It should be included in the test cases.

            """
            if keys is None:
                return None
            if len(keys) == 0:
                return []
            results = []

            if default is not None:
                results = map(lambda key, myself=self,
                    mydefault=default: myself.valueForName(key, mydefault), keys)
            elif defaults is not None:
                if len(keys) is not len(defaults):
                    raise NamedValueAccessError, \
                        'Keys and defaults have mismatching lengths (%d and %d).' \
                        % (len(keys), len(defaults))
                results = map(lambda key, default,
                    myself=self: myself.valueForName(key, default), keys, defaults)
            elif forgive:
                results = []
                uniqueObject = 'uni' + 'que'
                for key in keys:
                    value = self.valueForName(key, uniqueObject)
                    if value is not uniqueObject:
                        if includeNames:
                            results.append((key, value))
                        else:
                            results.append(value)
            else:
                # no defaults, no forgiveness
                results = map(lambda key,
                    myself=self: myself.valueForName(key), keys)
            return results

        def setValueForKey(self, key, value):
            """Set value for a given key.

            Suppose key is 'foo'.
            This method sets the value with the following precedence:
                1. Public attributes before private attributes
                2. Methods before non-methods

            More specifically, this method then uses one of the following:
                @@ 2000-03-04 ce: fill in

            ... or invokes handleUnknownSetKey().

            """
            raise NotImplementedError # @@ 2000-03-04 ce

        def resetKeyBindings(self):
            """Rest all key bindings, releasing alreaedy referenced values."""
            if hasattr(self, '_kvGetBindings'):
                self._kvGetBindings = {}

        ## Errors ##

        def valueForUnknownKey(self, key, default):
            raise NamedValueAccessError, key

        def handleUnknownSetKey(self, key):
            raise NamedValueAccessError, key

        ## Private ##

        def _bindingForGetKey(self, key):
            """Get binding for given key.

            Bindings are cached. Bindings are methods or strings.

            """

            # Make _kvGetBindings dictionary if we don't have one
            if not hasattr(self, '_kvGetBindings'):
                self._kvGetBindings = {}

            # Return the binding if we already have one
            if self._kvGetBindings.has_key(key):
                return self._kvGetBindings[key]

            # No binding, so we have to look for the key

            found = None  # set to what we find

            # Try plain old key
            if hasattr(self, key):
                found = getattr(self, key)
                if type(found) is not types.MethodType:
                    found = key
                elif technique:
                    found = getattr(self.__class__, key)
                self._kvGetBindings[key] = found

            # Try _key only if we didn't find a method called key
            if type(found) is not types.MethodType:
                underKey = '_' + key
                if hasattr(self, underKey):
                    underAttr = getattr(self, underKey)
                    if found is None:
                        if type(underAttr) is types.MethodType:
                            if technique:
                                value = getattr(self.__class__, underKey)
                            else:
                                value = underAttr
                        else:
                            value = underKey
                        found = self._kvGetBindings[key] = value
                    else:
                        if type(underAttr) is types.MethodType:
                            if technique:
                                underAttr = getattr(self.__class__, underKey)
                            found = self._kvGetBindings[key] = underAttr

            return found

    class NamedValueAccessWrapper(NamedValueAccess):
        """Mix-in class for accessing Python objects by named attributes.

        This provides a wrapper around an existing object which will respond
        to the methods of NamedValueAccess. By using the wrapper, you can
        stick with objects and methods such as obj.valueForName('x.y') (as
        opposed to functions like valueForName()) and refrain from modifying
        the existing class hierarchy with NamedValueAccess.

        Example:
            wrapper = NamedValueAccessWrapper(obj)
            print wrapper.valueForName('manager.name')

        """

        def __init__(self, object):
            self._object = object

        def hasValueForKey(self, key):
            try:
                self.valueForKey(key)
            except NamedValueAccessError:
                return 0
            else:
                return 1

        def valueForKey(self, key, default=NoDefault):
            return valueForKey(self._object)

        def valueForName(self, key, default=NoDefault):
            return valueForName(self._object)

    ## Private ##

    def _valueForKeySequence(obj, listOfKeys, default=None):
        """Get the value of an object for a given list of keys.

        This is a recursive function used to implement
        NamedValueAccess.valueForKeySequence.
        Besides supporting inheritors of NamedValueAccess, this function also
        supports dictionaries, which is why it's not found in the class.

        """

        # @@ 2000-02-18: Optimize by specifying index instead of making new list
        if type(obj) is types.DictType:
            try:
                value = obj[listOfKeys[0]]
            except KeyError:
                if default is None:
                    raise NamedValueAccessError, \
                        'Unknown key (%s) in dictionary.' % listOfKeys[0]
                else:
                    return default
        else:
            value = obj.valueForKey(listOfKeys[0], default)
        if len(listOfKeys) > 1:
            return _valueForKeySequence(value, listOfKeys[1:], default)
        else:
            return value

    def _dict_valueForKey(obj, key, default=NoDefault):
        """Get the value of a dict-like object for a given key.

        Returns the value for a given key of the dictionary-like object.
        This is a private, custom function built in support of valueForKey().

        """
        try:
            value = obj[key]
        except AttributeError, e:
            # We attempt to pass only on exceptions caused
            # by obj not responding to __getitem__.
            # Any other exceptions generated get raised up.
            substring = "instance has no attribute '__getitem__'"
            if e.args[0][-len(substring):] == substring:
                if default is NoDefault:
                    return None
                else:
                    return
            else:
                raise
        except KeyError, e:
            if e.args[0] == key:
                if default is NoDefault:
                    raise ValueForKeyError, key
                else:
                    return default
            else:
                # If we get here, then the KeyError is deeper in the
                # implementation of obj[key]
                raise
        else:
            return value

    def valueForKey(obj, key, default=NoDefault):
        """Get the value of the object named by the given key.

        Suppose key is 'foo'.
        This method returns the value with the following precedence:
            1. Methods before non-methods
            2. Attributes before keys (__getitem__)
            3. Public things before private things
               (private being denoted by a preceding underscore)

        More specifically, this method returns one of the following:
            * obj.valueForKey(key)  # only if the method exists
            * obj.foo()
            * obj._foo()
            * obj.foo
            * obj._foo
            * obj['foo']
            * obj.valueForUnknownKey(key)
            * default  # only if specified

        If all of these fail, a ValueForKeyError is raised.

        NOTES

        * If the object provides a valueForKey() method, that method will be
          invoked to do the work.

        * valueForKey() works on dictionaries and dictionary-like objects.

        * valueForUnknownKey() provides a hook by which objects can
          delegate or chain their keyed value access to other objects.
          The key and default arguments are passed to it and it should
          generally respect the typical treatment of the the default
          argument as found throughout Webware and described in the Style
          Guidelines.

        * See valueForName() which is a more advanced version of this
          function that allows multiple, qualified keys.

        """

        assert obj is not None

        # We only accept strings for keys
        assert type(key) is types.StringType

        # Use obj.valueForKey() if it is available
        valueForKeyMeth = getattr(obj, 'valueForKey', None)
        if valueForKeyMeth:
            return valueForKeyMeth(key, default)

        attr   = None
        method = None
        unknown = 0
        if type(obj) is types.DictType:
            if default is NoDefault:
                try:
                    return obj[key]
                except KeyError:
                    raise ValueForKeyError, key
            else:
                return obj.get(key, default)
        else:
            try:
                klass = obj.__class__
            except AttributeError:
                # happens for classes themselves
                klass = None
                method = None
            else:
                method = getattr(klass, key, None)
            if not method:
                underKey = '_' + key
                method = klass and getattr(klass, underKey, None) or None
                if not method:
                    attr = getattr(obj, key, NoDefault)
                    if attr is NoDefault:
                        attr = getattr(obj, underKey, NoDefault)
                        if attr is NoDefault:
                            if klass is not None:
                                getitem = getattr(klass, '__getitem__', None)
                                if getitem:
                                    try:
                                        getitem(obj, key)
                                    except KeyError:
                                        unknown = 1

        if not unknown:
            if method:
                return method(obj)
            if attr is not NoDefault:
                return attr

        # Use obj.valueForUnknownKey() if it is available
        valueForUnknownKey = getattr(obj, 'valueForUnknownKey', None)
        if valueForUnknownKey:
            return valueForUnknownKey(key, default)

        if default is not NoDefault:
            return default
        else:
            raise ValueForKeyError, key

    def valueForName(obj, name, default=NoDefault):
        """Get the value of the object that is named.

        The name can use dotted notation to traverse through a network/graph
        of objects. Since this function relies on valueForKey() for each
        individual component of the name, you should be familiar with the
        semantics of that notation.

        Example: valueForName(obj, 'department.manager.salary')

        """
        names = name.split('.')
        for name in names:
            obj = valueForKey(obj, name, default)
            if obj is default:
                return obj
            # 2001-04-19 ce: I suppose the above technique could result in
            # the default being returned prematurely if it was part of the
            # chain of names. Well, that's just the way it goes for now.
        return obj

    # Beef up UserDict with the NamedValueAccess base class and custom versions of
    # hasValueForKey() and valueForKey(). This all means that UserDict's (such as
    # os.environ) are key/value accessible.
    # @@ 2000-05-07 ce: CGIWrapper.py duplicates this.
    def _enhanceUserDict():
        from UserDict import UserDict
        if not NamedValueAccess in UserDict.__bases__:
            UserDict.__bases__ += (NamedValueAccess,)

            def _UserDict_hasValueForKey(self, key):
                return self.has_key(key)

            def _UserDict_valueForKey(self, key, default=NoDefault):
                if default is NoDefault:
                    if self.has_key(key):
                        return self[key]
                    else:
                        raise ValueForKeyError, key
                else:
                    return self.get(key, default)

            setattr(UserDict, 'hasValueForKey', _UserDict_hasValueForKey)
            setattr(UserDict, 'valueForKey', _UserDict_valueForKey)

    _enhanceUserDict()