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# -*- coding: utf-8 -*-
# Copyright (c) 2010 Mark Sandstrom
# Copyright (c) 2011-2013 Raphaël Barrois
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
import logging
logger = logging.getLogger(__name__)
from . import declarations
from . import utils
class CyclicDefinitionError(Exception):
"""Raised when cyclic definition were found."""
class LazyStub(object):
"""A generic container that only allows getting attributes.
Attributes are set at instantiation time, values are computed lazily.
Attributes:
__initialized (bool): whether this object's __init__ as run. If set,
setting any attribute will be prevented.
__attrs (dict): maps attribute name to their declaration
__values (dict): maps attribute name to computed value
__pending (str list): names of the attributes whose value is being
computed. This allows to detect cyclic lazy attribute definition.
__containers (LazyStub list): "parents" of the LazyStub being built.
This allows to have the field of a field depend on the value of
another field
__model_class (type): the model class to build.
"""
__initialized = False
def __init__(self, attrs, containers=(), model_class=object, log_ctx=None):
self.__attrs = attrs
self.__values = {}
self.__pending = []
self.__containers = containers
self.__model_class = model_class
self.__log_ctx = log_ctx or '%s.%s' % (model_class.__module__, model_class.__name__)
self.factory_parent = containers[0] if containers else None
self.__initialized = True
def __repr__(self):
return '<LazyStub for %s.%s>' % (self.__model_class.__module__, self.__model_class.__name__)
def __str__(self):
return '<LazyStub for %s with %s>' % (
self.__model_class.__name__, list(self.__attrs.keys()))
def __fill__(self):
"""Fill this LazyStub, computing values of all defined attributes.
Retunrs:
dict: map of attribute name => computed value
"""
res = {}
logger.debug("LazyStub: Computing values for %s(%s)",
self.__log_ctx, utils.log_pprint(kwargs=self.__attrs),
)
for attr in self.__attrs:
res[attr] = getattr(self, attr)
logger.debug("LazyStub: Computed values, got %s(%s)",
self.__log_ctx, utils.log_pprint(kwargs=res),
)
return res
def __getattr__(self, name):
"""Retrieve an attribute's value.
This will compute it if needed, unless it is already on the list of
attributes being computed.
"""
if name in self.__pending:
raise CyclicDefinitionError(
"Cyclic lazy attribute definition for %s; cycle found in %r." %
(name, self.__pending))
elif name in self.__values:
return self.__values[name]
elif name in self.__attrs:
val = self.__attrs[name]
if isinstance(val, LazyValue):
self.__pending.append(name)
val = val.evaluate(self, self.__containers)
last = self.__pending.pop()
assert name == last
self.__values[name] = val
return val
else:
raise AttributeError(
"The parameter %s is unknown. Evaluated attributes are %r, "
"definitions are %r." % (name, self.__values, self.__attrs))
def __setattr__(self, name, value):
"""Prevent setting attributes once __init__ is done."""
if not self.__initialized:
return super(LazyStub, self).__setattr__(name, value)
else:
raise AttributeError('Setting of object attributes is not allowed')
class LazyValue(object):
"""Some kind of "lazy evaluating" object."""
def evaluate(self, obj, containers=()): # pragma: no cover
"""Compute the value, using the given object."""
raise NotImplementedError("This is an abstract method.")
class OrderedDeclarationWrapper(LazyValue):
"""Lazy wrapper around an OrderedDeclaration.
Attributes:
declaration (declarations.OrderedDeclaration): the OrderedDeclaration
being wrapped
sequence (int): the sequence counter to use when evaluatin the
declaration
"""
def __init__(self, declaration, sequence, create, extra=None, **kwargs):
super(OrderedDeclarationWrapper, self).__init__(**kwargs)
self.declaration = declaration
self.sequence = sequence
self.create = create
self.extra = extra
def evaluate(self, obj, containers=()):
"""Lazily evaluate the attached OrderedDeclaration.
Args:
obj (LazyStub): the object being built
containers (object list): the chain of containers of the object
being built, its immediate holder being first.
"""
return self.declaration.evaluate(self.sequence, obj,
create=self.create,
extra=self.extra,
containers=containers,
)
def __repr__(self):
return '<%s for %r>' % (self.__class__.__name__, self.declaration)
class AttributeBuilder(object):
"""Builds attributes from a factory and extra data.
Attributes:
factory (base.Factory): the Factory for which attributes are being
built
_attrs (DeclarationDict): the attribute declarations for the factory
_subfields (dict): dict mapping an attribute name to a dict of
overridden default values for the related SubFactory.
"""
def __init__(self, factory, extra=None, log_ctx=None, **kwargs):
super(AttributeBuilder, self).__init__(**kwargs)
if not extra:
extra = {}
self.factory = factory
self._containers = extra.pop('__containers', ())
self._attrs = factory.declarations(extra)
self._log_ctx = log_ctx
initial_declarations = factory.declarations({})
attrs_with_subfields = [
k for k, v in initial_declarations.items()
if self.has_subfields(v)]
self._subfields = utils.multi_extract_dict(
attrs_with_subfields, self._attrs)
def has_subfields(self, value):
return isinstance(value, declarations.ParameteredAttribute)
def build(self, create, force_sequence=None):
"""Build a dictionary of attributes.
Args:
create (bool): whether to 'build' or 'create' the subfactories.
force_sequence (int or None): if set to an int, use this value for
the sequence counter; don't advance the related counter.
"""
# Setup factory sequence.
if force_sequence is None:
sequence = self.factory._generate_next_sequence()
else:
sequence = force_sequence
# Parse attribute declarations, wrapping SubFactory and
# OrderedDeclaration.
wrapped_attrs = {}
for k, v in self._attrs.items():
if isinstance(v, declarations.OrderedDeclaration):
v = OrderedDeclarationWrapper(v,
sequence=sequence,
create=create,
extra=self._subfields.get(k, {}),
)
wrapped_attrs[k] = v
stub = LazyStub(wrapped_attrs, containers=self._containers,
model_class=self.factory, log_ctx=self._log_ctx)
return stub.__fill__()
class StubObject(object):
"""A generic container."""
pass
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