"""
Declarative objects.
Declarative objects have a simple protocol: you can use classes in
lieu of instances and they are equivalent, and any keyword arguments
you give to the constructor will override those instance variables.
(So if a class is received, we'll simply instantiate an instance with
no arguments).
You can provide a variable __unpackargs__ (a list of strings), and if
the constructor is called with non-keyword arguments they will be
interpreted as the given keyword arguments.
If __unpackargs__ is ('*', name), then all the arguments will be put
in a variable by that name.
You can define a __classinit__(cls, new_attrs) method, which will be
called when the class is created (including subclasses). Note: you
can't use super() in __classinit__ because the class isn't bound to a
name. As an analog to __classinit__, Declarative adds
__instanceinit__ which is called with the same argument (new_attrs).
This is like __init__, but after __unpackargs__ and other factors have
been taken into account.
If __mutableattributes__ is defined as a sequence of strings, these
attributes will not be shared between superclasses and their
subclasses. E.g., if you have a class variable that contains a list
and you append to that list, changes to subclasses will effect
superclasses unless you add the attribute here.
Also defines classinstancemethod, which acts as either a class method
or an instance method depending on where it is called.
"""
import copy
import events
import itertools
counter = itertools.count()
__all__ = ('classinstancemethod', 'DeclarativeMeta', 'Declarative')
class classinstancemethod(object):
"""
Acts like a class method when called from a class, like an
instance method when called by an instance. The method should
take two arguments, 'self' and 'cls'; one of these will be None
depending on how the method was called.
"""
def __init__(self, func):
self.func = func
def __get__(self, obj, type=None):
return _methodwrapper(self.func, obj=obj, type=type)
class _methodwrapper(object):
def __init__(self, func, obj, type):
self.func = func
self.obj = obj
self.type = type
def __call__(self, *args, **kw):
assert not kw.has_key('self') and not kw.has_key('cls'), (
"You cannot use 'self' or 'cls' arguments to a "
"classinstancemethod")
return self.func(*((self.obj, self.type) + args), **kw)
def __repr__(self):
if self.obj is None:
return ('<bound class method %s.%s>'
% (self.type.__name__, self.func.func_name))
else:
return ('<bound method %s.%s of %r>'
% (self.type.__name__, self.func.func_name, self.obj))
class DeclarativeMeta(type):
def __new__(meta, class_name, bases, new_attrs):
post_funcs = []
early_funcs = []
events.send(events.ClassCreateSignal,
bases[0], class_name, bases, new_attrs,
post_funcs, early_funcs)
cls = type.__new__(meta, class_name, bases, new_attrs)
for func in early_funcs:
func(cls)
if new_attrs.has_key('__classinit__'):
cls.__classinit__ = staticmethod(cls.__classinit__.im_func)
cls.__classinit__(cls, new_attrs)
for func in post_funcs:
func(cls)
return cls
class Declarative(object):
__unpackargs__ = ()
__mutableattributes__ = ()
__metaclass__ = DeclarativeMeta
__restrict_attributes__ = None
def __classinit__(cls, new_attrs):
cls.declarative_count = counter.next()
for name in cls.__mutableattributes__:
if not new_attrs.has_key(name):
setattr(cls, copy.copy(getattr(cls, name)))
def __instanceinit__(self, new_attrs):
if self.__restrict_attributes__ is not None:
for name in new_attrs:
if name not in self.__restrict_attributes__:
raise TypeError(
'%s() got an unexpected keyword argument %r'
% (self.__class__.__name__, name))
for name, value in new_attrs.items():
setattr(self, name, value)
if not new_attrs.has_key('declarative_count'):
self.declarative_count = counter.next()
def __init__(self, *args, **kw):
if self.__unpackargs__ and self.__unpackargs__[0] == '*':
assert len(self.__unpackargs__) == 2, \
"When using __unpackargs__ = ('*', varname), you must only provide a single variable name (you gave %r)" % self.__unpackargs__
name = self.__unpackargs__[1]
if kw.has_key(name):
raise TypeError(
"keyword parameter '%s' was given by position and name"
% name)
kw[name] = args
else:
if len(args) > len(self.__unpackargs__):
raise TypeError(
'%s() takes at most %i arguments (%i given)'
% (self.__class__.__name__,
len(self.__unpackargs__),
len(args)))
for name, arg in zip(self.__unpackargs__, args):
if kw.has_key(name):
raise TypeError(
"keyword parameter '%s' was given by position and name"
% name)
kw[name] = arg
if kw.has_key('__alsocopy'):
for name, value in kw['__alsocopy'].items():
if not kw.has_key(name):
if name in self.__mutableattributes__:
value = copy.copy(value)
kw[name] = value
del kw['__alsocopy']
self.__instanceinit__(kw)
def __call__(self, *args, **kw):
kw['__alsocopy'] = self.__dict__
return self.__class__(*args, **kw)
def singleton(self, cls):
if self:
return self
name = '_%s__singleton' % cls.__name__
if not hasattr(cls, name):
setattr(cls, name, cls(declarative_count=cls.declarative_count))
return getattr(cls, name)
singleton = classinstancemethod(singleton)
def __repr__(self, cls):
if self:
name = '%s object' % self.__class__.__name__
v = self.__dict__.copy()
else:
name = '%s class' % cls.__name__
v = cls.__dict__.copy()
if v.has_key('declarative_count'):
name = '%s %i' % (name, v['declarative_count'])
del v['declarative_count']
# @@: simplifying repr:
#v = {}
names = v.keys()
args = []
for n in self._repr_vars(names):
args.append('%s=%r' % (n, v[n]))
if not args:
return '<%s>' % name
else:
return '<%s %s>' % (name, ' '.join(args))
def _repr_vars(dictNames):
names = [n for n in dictNames
if not n.startswith('_')
and n != 'declarative_count']
names.sort()
return names
_repr_vars = staticmethod(_repr_vars)
__repr__ = classinstancemethod(__repr__)
def setup_attributes(cls, new_attrs):
for name, value in new_attrs.items():
if hasattr(value, '__addtoclass__'):
value.__addtoclass__(cls, name)
|