python-pastewebkit 1.0-7 / usr / share / pyshared / paste / webkit / FakeWebware / MiscUtils / NamedValueAccess.py

"""
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

* Docs: More improvs to doc strings.

* Testing: increase coverage

* Rename? class NamedValueAccess+ible:

* Benchmarking: Set this up in a new file:
	Testing/BenchNamedValueAccess.py
  so we can experment 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
import string, sys
from time import time
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:
	"""
	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 ivars 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
	(other than typical things like string and sys).

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

	You can run the test suite by running this module as a program.

	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 ivars

	@@ 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):
		"""	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)!=None


	def valueForKey(self, key, default=NoDefault):
		""" 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:
# @@ 2000-05-07 ce: come to a decision on exception handling for key errors
#			try:
			if technique:
				result = binding(self)
			else:
				result = binding()
#			except:
				# @@ 2000-02-18: Improve next line with exception info
#				raise NamedValueAccessError, 'Caught exception while accessing key (%s). Exception is %s' % (key, sys.exc_info())
			return result
		else:
			return getattr(self, binding)

	def hasValueForName(self, keysString):
		try:
			value = self.valueForName(keysString)
		except NamedValueAccessError:
			return 0
		return 1

	def valueForName(self, keysString, default=None):
		""" Returns 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 = string.split(keysString, '.')
		return self.valueForKeySequence(keys, default)

	def valueForKeySequence(self, listOfKeys, default=None):
		# @@ 2000-02-18: document
		return _valueForKeySequence(self, listOfKeys, default)

	def valuesForNames(self, keys, default=None, defaults=None, forgive=0, includeNames=0):
		""" 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 is a sequence. default is any kind of object. defaults is a sequence.
			  forgive and includeNames is a flag.
			If default is not None, then it is substituted when a key is not found.
			Otherwise, if defaults is not None, then it's corresponding/parallel value
			  for the current key is substituted when a key is not found.
			Otherwise, if forgive=1, then unknown keys simply don't produce any values.
			Otherwise, if default and defaults are None, and forgive=0, 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) is 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):
		# @@ 2000-02-18: naming might be weired here with args reversed
		""" 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):
		# @@ 2000-02-18 document this method
		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):
		"""	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)
			#print '0: found = ', found, type(found)
			if type(found) is not types.MethodType:
				found = key
			elif technique:
				found = getattr(self.__class__, key)
			self._kvGetBindings[key] = found
		#print '1: found = ', found, type(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==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

		#print '2: found = ', found, type(found)

		return found


class NamedValueAccessWrapper(NamedValueAccess):
	"""
	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:
			value = self.valueForKey(ley)
		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):
	"""	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: # @@ 2000-03-03 ce: this exception should be more specific. probably nameerror or indexerror
			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):
	"""
	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):
	"""
	Returns 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.
	"""

	# 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
	value  = 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:
			raise AttributeError, '__class__ obj type=%r, obj=%r' % (type(obj), obj)
		method   = getattr(klass, key, None)
		if not method:
			underKey = '_' + key
			method = getattr(klass, underKey, None)
			if not method:
				attr = getattr(obj, key, NoDefault)
				if attr is NoDefault:
					attr = getattr(obj, underKey, NoDefault)
					if attr is NoDefault:
						getitem = getattr(obj.__class__, '__getitem__', None)
						if getitem:
							try:
								value = getitem(obj, key)
							except KeyError:
								unknown = 1

#	if value is not NoDefault:
#		return value
	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!=NoDefault:
		return default
	else:
		raise ValueForKeyError, key


def valueForName(obj, name, default=NoDefault):
	"""
	Returns 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 = string.split(name, '.')
	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__ = 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()