t.s.jelly : module documentation

Part of twisted.spread View Source

S-expression-based persistence of python objects.

It does something very much like Pickle; however, pickle's main goal seems to be efficiency (both in space and time); jelly's main goals are security, human readability, and portability to other environments.

This is how Jelly converts various objects to s-expressions.

Boolean:

   True --> ['boolean', 'true']

Integer:

   1 --> 1

List:

   [1, 2] --> ['list', 1, 2]

String:

   "hello" --> "hello"

Float:

   2.3 --> 2.3

Dictionary:

   {'a': 1, 'b': 'c'} --> ['dictionary', ['b', 'c'], ['a', 1]]

Module:

   UserString --> ['module', 'UserString']

Class:

   UserString.UserString --> ['class', ['module', 'UserString'], 'UserString']

Function:

   string.join --> ['function', 'join', ['module', 'string']]

Instance: s is an instance of UserString.UserString, with a __dict__ {'data': 'hello'}:

   ["UserString.UserString", ['dictionary', ['data', 'hello']]]

Class Method: UserString.UserString.center:

   ['method', 'center', ['None'], ['class', ['module', 'UserString'],
    'UserString']]

Instance Method: s.center, where s is an instance of UserString.UserString:

   ['method', 'center', ['instance', ['reference', 1, ['class',
   ['module', 'UserString'], 'UserString']], ['dictionary', ['data', 'd']]],
   ['dereference', 1]]

The set builtin and the sets.Set class are serialized to the same thing, and unserialized to set if available, else to sets.Set. It means that there's a possibility of type switching in the serialization process. The solution is to always use set if possible, and only use sets.Set under Python 2.3; this can be accomplished by using twisted.python.compat.set.

The same rule applies for frozenset and sets.ImmutableSet.

AuthorGlyph Lefkowitz
Function setUnjellyableForClass Set which local class will represent a remote type.
Function setUnjellyableFactoryForClass

Set the factory to construct a remote instance of a type:


Function setUnjellyableForClassTree Set all classes in a module derived from baseClass as copiers for a corresponding remote class.
Function getInstanceState Utility method to default to 'normal' state rules in serialization.
Function setInstanceState Utility method to default to 'normal' state rules in unserialization.
Class Unpersistable This is an instance of a class that comes back when something couldn't be unpersisted.
Class Jellyable Inherit from me to Jelly yourself directly with the `getStateFor' convenience method.
Class Unjellyable Inherit from me to Unjelly yourself directly with the setStateFor convenience method.
Class InsecureJelly This exception will be raised when a jelly is deemed `insecure'; e.g. it contains a type, class, or module disallowed by the specified `taster'
Class DummySecurityOptions DummySecurityOptions() -> insecure security options Dummy security options -- this class will allow anything.
Class SecurityOptions This will by default disallow everything, except for 'none'.
Function jelly Serialize to s-expression.
Function unjelly Unserialize from s-expression.
Function _newInstance Make a new instance of a class without calling its __init__ method. Supports both new- and old-style classes.
Function _maybeClass Undocumented
Class _Jellier (Internal) This class manages state for a call to jelly()
Class _Unjellier No class docstring; 5/27 methods documented
Class _Dummy (Internal) Dummy class, used for unserializing instances.
Class _DummyNewStyle (Internal) Dummy class, used for unserializing instances of new-style classes.
Function _newDummyLike Create a new instance like instance.
def _newInstance(cls, state=_NO_STATE): (source)
Make a new instance of a class without calling its __init__ method. Supports both new- and old-style classes.
ParametersstateA dict used to update inst.__dict__ or _NO_STATE to skip this part of initialization.
ReturnsA new instance of cls.
def _maybeClass(classnamep): (source)
Undocumented
def setUnjellyableForClass(classname, unjellyable): (source)
Set which local class will represent a remote type.

If you have written a Copyable class that you expect your client to be receiving, write a local "copy" class to represent it, then call:

   jellier.setUnjellyableForClass('module.package.Class', MyCopier).

Call this at the module level immediately after its class definition. MyCopier should be a subclass of RemoteCopy.

The classname may be a special tag returned by 'Copyable.getTypeToCopyFor' rather than an actual classname.

This call is also for cached classes, since there will be no overlap. The rules are the same.

def setUnjellyableFactoryForClass(classname, copyFactory): (source)
Set the factory to construct a remote instance of a type:

 jellier.setUnjellyableFactoryForClass('module.package.Class', MyFactory)

Call this at the module level immediately after its class definition. copyFactory should return an instance or subclass of RemoteCopy.

Similar to setUnjellyableForClass except it uses a factory instead of creating an instance.

def setUnjellyableForClassTree(module, baseClass, prefix=None): (source)
Set all classes in a module derived from baseClass as copiers for a corresponding remote class.

When you have a heirarchy of Copyable (or Cacheable) classes on one side, and a mirror structure of Copied (or RemoteCache) classes on the other, use this to setUnjellyableForClass all your Copieds for the Copyables.

Each copyTag (the "classname" argument to getTypeToCopyFor, and what the Copyable's getTypeToCopyFor returns) is formed from adding a prefix to the Copied's class name. The prefix defaults to module.__name__. If you wish the copy tag to consist of solely the classname, pass the empty string ''.

Parametersmodulea module object from which to pull the Copied classes. (passing sys.modules[__name__] might be useful)
baseClassthe base class from which all your Copied classes derive.
prefixthe string prefixed to classnames to form the unjellyableRegistry.
def getInstanceState(inst, jellier): (source)
Utility method to default to 'normal' state rules in serialization.
def setInstanceState(inst, unjellier, jellyList): (source)
Utility method to default to 'normal' state rules in unserialization.
def _newDummyLike(instance): (source)
Create a new instance like instance.

The new instance has the same class and instance dictionary as the given instance.

ReturnsThe new instance.
def jelly(object, taster=DummySecurityOptions(), persistentStore=None, invoker=None): (source)
Serialize to s-expression.

Returns a list which is the serialized representation of an object. An optional 'taster' argument takes a SecurityOptions and will mark any insecure objects as unpersistable rather than serializing them.

def unjelly(sexp, taster=DummySecurityOptions(), persistentLoad=None, invoker=None): (source)
Unserialize from s-expression.

Takes an list that was the result from a call to jelly() and unserializes an arbitrary object from it. The optional 'taster' argument, an instance of SecurityOptions, will cause an InsecureJelly exception to be raised if a disallowed type, module, or class attempted to unserialize.

API Documentation for Twisted, generated by pydoctor at 2012-06-04 17:20:01.