pyecore 0.1.5

A Python(ic) Implementation of the Eclipse Modeling Framework (EMF/Ecore)

PyEcore is a “Pythonic?” (sounds pretentious) implementation of EMF/Ecore for Python3. It’s purpose is to handle model/metamodels in Python almost the same way the Java version does.

However, PyEcore enables you to use a simple instance.attribute notation instead of instance.setAttribute(...)/getAttribute(...) for the Java version. To achieve this, PyEcore relies on reflection (a lot).

Let see by yourself how it works on a very simple metamodel created on the fly (dynamic metamodel):

>>> from pyecore.ecore import EClass, EAttribute, EString, EObject
>>> A = EClass('A')  # We create metaclass named 'A'
>>> A.eStructuralFeatures.append(EAttribute('myname', EString, default_value='new_name')) # We add a name attribute to the A metaclass
>>> a1 = A()  # We create an instance
>>> a1.myname
'new_name'
>>> a1.myname = 'a_instance'
>>> a1.myname
'a_instance'
>>> isinstance(a1, EObject)
True

PyEcore also support introspection and the EMF reflexive API using basic Python reflexive features:

>>> a1.eClass # some introspection
<EClass name="A">
>>> a1.eClass.eClass
<EClass name="EClass">
>>> a1.eClass.eClass is a1.eClass.eClass.eClass
True
>>> a1.eClass.eStructuralFeatures
(<pyecore.ecore.EAttribute at 0x7f6bf6cd91d0>,)
>>> a1.eClass.eStructuralFeatures[0].name
'myname'
>>> a1.eClass.eStructuralFeatures[0].eClass
<EClass name="EAttribute">
>>> a1.__getattribute__('name')
'a_instance'
>>> a1.__setattr__('myname', 'reflexive')
>>> a1.__getattribute__('myname')
'reflexive'
>>> a1.eSet('myname', 'newname')
>>> a1.eGet('myname')
'newname'

Runtime type checking is also performed (regarding what you expressed in your) metamodel:

>>> a1.myname = 1
Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File ".../pyecore/ecore.py", line 66, in setattr
        raise BadValueError(got=value, expected=estruct.eType)
pyecore.ecore.BadValueError: Expected type EString(str), but got type int with value 1 instead

PyEcore does support dynamic metamodel and static ones (see details in next sections).

The project is at an early stage and still requires more love.

Contents

• Dynamic Metamodels

• Static Metamodels

• Static/Dynamic EOperation

• Notifications

• Deep Journey Inside PyEcore

  • EClasse Instances as Factories

• Importing an Existing XMI Metamodel/Model

  • Adding External Metamodel Resources

  • Metamodel References by ‘File Path’

  • Adding External resources

• Exporting an Existing XMI Resource

• Deleting Elements

  • The delete() method

  • Removing an element from it’s container

• Installation

• Dependencies

• Run the Tests

• Liberty Regarding the Java EMF Implementation

• State

• Existing Projects

• Additional Resources

Dynamic Metamodels

Dynamic metamodels reflects the ability to create metamodels “on-the-fly”. You can create metaclass hierarchie, add EAttribute and EReference.

In order to create a new metaclass, you need to create an EClass instance:

>>> import pyecore.ecore as Ecore
>>> MyMetaclass = Ecore.EClass('MyMetaclass')

You can then create instances of your metaclass:

>>> instance1 = MyMetaclass()
>>> instance2 = MyMetaclass()
>>> assert instance1 is not instance2

>From the created instances, we can go back to the metaclasses:

>>> instance1.eClass
<EClass name="MyMetaclass">

Then, we can add metaproperties to the freshly created metaclass:

>>> instance1.eClass.eAttributes
[]
>>> MyMetaclass.eStructuralFeatures.append(Ecore.EAttribute('name', Ecore.EString))
>>> instance1.eClass.eStructuralFeatures
[<pyecore.ecore.EAttribute object at 0x7f7da72ba940>]
>>> str(instance1.name)
'None'
>>> instance1.name = 'mystuff'
>>> instance1.name
'mystuff'

We can also create a new metaclass B and a new metareferences towards B:

>>> B = Ecore.EClass('B')
>>> MyMetaclass.eStructuralFeatures.append(Ecore.EReference('toB', B, containment=True))
>>> b1 = B()
>>> instance1.toB = b1
>>> instance1.toB
<pyecore.ecore.B object at 0x7f7da70531d0>
>>> b1.eContainer() is instance1   # because 'toB' is a containment reference
True

Opposite and ‘collection’ meta-references are also managed:

>>> C = Ecore.EClass('C')
>>> C.eStructuralFeatures.append(Ecore.EReference('toMy', MyMetaclass))
>>> MyMetaclass.eStructuralFeatures.append(Ecore.EReference('toCs', C, upper=-1, eOpposite=C.eStructuralFeatures[0]))
>>> instance1.toCs
[]
>>> c1 = C()
>>> c1.toMy = instance1
>>> instance1.toCs  # 'toCs' should contain 'c1' because 'toMy' is opposite relation of 'toCs'
[<pyecore.ecore.C object at 0x7f7da7053390>]

Static Metamodels

The static definition of a metamodel using PyEcore mostly relies on the classical classes definitions in Python. The following example is more related to a ‘by hand’ static metamodel definition. This way of producing metamodels is kinda deprecated as a MTL generator (in /generator) automatically produces a static metamodel from the .ecore definition.

$ cat example.py
"""
static metamodel example
"""
from pyecore.ecore import EObject, EAttribute, EReference, EString, MetaEClass

nsURI = 'http://example/1.0'


class B(EObject, metaclass=MetaEClass):
    def __init__(self):
        pass


class C(EObject, metaclass=MetaEClass):
    def __init__(self):
        pass


class MyMetaclass(EObject, metaclass=MetaEClass):
    name = EAttribute(eType=EString)
    toB = EReference(eType=B, containment=True)
    toCs = EReference(eType=C, upper=-1)

    def __init__(self):
        pass

# We need to update C in order to add the opposite meta-reference
# At the moment, the information need to be added in two places
C.toMy = EReference('toMy', MyMetaclass, eOpposite=MyMetaclass.toCs)
C.eClass.eStructuralFeatures.append(C.toMy)

$ python
...
>>> import example
>>> instance1 = example.MyMetaclass()
>>> c1 = C()
>>> c1.toMy = instance1
>>> assert c1 is instance1.toCs[0] and c1.toMy is instance1

The automatic code generator defines a Python package hierarchie instead of only a Python module. This allows more freedom for dedicated operations and references between packages.

Static/Dynamic EOperation

PyEcore also support EOperation definition for static and dynamic metamodel. For static metamodel, the solution is simple, a simple method with the code is added inside the defined class. The corresponding EOperation is created on the fly. Theire is still some “requirements” for this. In order to be understood as an EOperation candidate, the defined method must have at least one parameter and the first parameter must always be named self.

For dynamic metamodels, the simple fact of adding an EOperation instance in the EClass instance, adds an “empty” implementation:

>>> import pyecore.ecore as Ecore
>>> A = Ecore.EClass('A')
>>> operation = Ecore.EOperation('myoperation')
>>> param1 = Ecore.EParameter('param1', eType=Ecore.EString, required=True)
>>> operation.eParameters.append(param1)
>>> A.eOperations.append(operation)
>>> a = A()
>>> help(a.myoperation)
Help on method myoperation:

myoperation(param1) method of pyecore.ecore.A instance
>>> a.myoperation('test')
...
NotImplementedError: Method myoperation(param1) is not yet implemented

For each EParameter, the required parameter express the fact that the parameter is required or not in the produced operation:

>>> operation2 = Ecore.EOperation('myoperation2')
>>> p1 = Ecore.EParameter('p1', eType=Ecore.EString)
>>> operation2.eParameters.append(p1)
>>> A.eOperations.append(operation2)
>>> a = A()
>>> a.operation2(p1='test')  # Will raise a NotImplementedError exception

You can then create an implementation for the eoperation and link it to the EClass:

>>> def myoperation(self, param1):
...:    print(self, param1)
...:
>>> A.python_class.myoperation = myoperation

To be able to propose a dynamic empty implementation of the operation, PyEcore relies on Python code generation at runtime.

Notifications

PyEcore gives you the ability to listen to modifications performed on an element. The EObserver class provides a basic observer which can receive notifications from the EObject it is register in:

>>> import library as lib  # we use the wikipedia library example
>>> from pyecore.notification import EObserver, Kind
>>> smith = lib.Writer()
>>> b1 = lib.Book()
>>> observer = EObserver(smith, notifyChanged=lambda x: print(x))
>>> b1.authors.append(smith)  # observer receive the notification from smith because 'authors' is eOpposite or 'books'

The EObserver notification method can be set using a lambda as in the previous example, using a regular function or by class inheritance:

>>> def print_notif(notification):
...:    print(notification)
...:
>>> observer = EObserver()
>>> observer.observe(b1)
>>> observer.notifyChanged = print_notif
>>> b1.authors.append(smith)  # observer receive the notification from b1

Using inheritance:

>>> class PrintNotification(EObserver):
...:    def __init__(self, notifier=None):
...:        super().__init__(notifier=notifier)
...:
...:    def notifyChanged(self, notification):
...:        print(notification)
...:
...:
>>> observer = PrintNotification(b1)
>>> b1.authors.append(smith)  # observer receive the notification from b1

The Notification object contains information about the performed modification:

• new -> the new added value (can be a collection) or None is remove or unset

• old -> the replaced value (always None for collections)

• feature -> the EStructuralFeature modified

• notifer -> the object that have been modified

• kind -> the kind of modification performed

The different kind of notifications that can be currently received are:

• ADD -> when an object is added to a collection

• ADD_MANY -> when many objects are added to a collection

• REMOVE -> when an object is removed from a collection

• SET -> when a value is set in an attribute/reference

• UNSET -> when a value is removed from an attribute/reference

Deep Journey Inside PyEcore

This section will provide some explanation of how PyEcore works.

EClasse Instances as Factories

The most noticeable difference between PyEcore and Java-EMF implementation is the fact that there is no factories (as you probably already seen). Each EClass instance is in itself a factory. This allows you to do this kind of tricks:

>>> A = EClass('A')
>>> eobject = A()  # We create an A instance
>>> eobject.eClass
<EClass name="A">
>>> eobject2 = eobject.eClass()  # We create another A instance
>>> assert isinstance(eobject2, eobject.__class__)
>>> from pyecore.ecore import EcoreUtils
>>> assert EcoreUtils.isinstance(eobject2, A)

In fact, each EClass instance create a new Python class named after the EClass name and keep a strong relationship towards it. Moreover, EClass implements is a callable and each time () is called on an EClass instance, an instance of the associated Python class is created. Here is a small example:

>>> MyClass = EClass('MyClass')  # We create an EClass instance
>>> type(MyClass)
pyecore.ecore.EClass
>>> MyClass.python_class
pyecore.ecore.MyClass
>>> myclass_instance = MyClass()  # MyClass is callable, creates an instance of the 'python_class' class
>>> myclass_instance
<pyecore.ecore.MyClass at 0x7f64b697df98>
>>> type(myclass_instance)
pyecore.ecore.MyClass
# We can access the EClass instance from the created instance and go back
>>> myclass_instance.eClass
<EClass name="MyClass">
>>> assert myclass_instance.eClass.python_class is MyClass.python_class
>>> assert myclass_instance.eClass.python_class.eClass is MyClass
>>> assert myclass_instance.__class__ is MyClass.python_class
>>> assert myclass_instance.__class__.eClass is MyClass
>>> assert myclass_instance.__class__.eClass is myclass_instance.eClass

The Python class hierarchie (inheritance tree) associated to the EClass instance

>>> B = EClass('B')  # in complement, we create a new B metaclass
>>> list(B.eAllSuperTypes())
[]
>>> B.eSuperTypes.append(A)  # B inherits from A
>>> list(B.eAllSuperTypes())
{<EClass name="A">}
>>> B.python_class.mro()
[pyecore.ecore.B,
 pyecore.ecore.A,
 pyecore.ecore.EObject,
 pyecore.ecore.ENotifier,
 object]
>>> b_instance = B()
>>> assert isinstance(b_instance, A.python_class)
>>> assert EcoreUtils.isinstance(b_instance, A)

Importing an Existing XMI Metamodel/Model

XMI support is still a work in progress, but the XMI import is on good tracks. Currently, only basic XMI metamodel (.ecore) and model instances can be loaded:

>>> from pyecore.resources import ResourceSet, URI
>>> rset = ResourceSet()
>>> resource = rset.get_resource(URI('path/to/mm.ecore'))
>>> mm_root = resource.contents[0]
>>> rset.metamodel_registry[mm_root.nsURI] = mm_root
>>> # At this point, the .ecore is loaded in the 'rset' as a metamodel
>>> resource = rset.get_resource(URI('path/to/instance.xmi'))
>>> model_root = resource.contents[0]
>>> # At this point, the model instance is loaded!

The ResourceSet/Resource/URI will evolve in the future. At the moment, only basic operations are enabled: create_resource/get_resource/load/save....

Adding External Metamodel Resources

External resources for metamodel loading should be added in the resource set. For example, some metamodels use the XMLType instead of the Ecore one. The resource creation should be done by hand first:

int_conversion = lambda x: int(x)  # translating str to int durint load()
String = Ecore.EDataType('String', str)
Double = Ecore.EDataType('Double', int, 0, from_string=int_conversion)
Int = Ecore.EDataType('Int', int, from_string=int_conversion)
IntObject = Ecore.EDataType('IntObject', int, None,
                            from_string=int_conversion)
Boolean = Ecore.EDataType('Boolean', bool, False,
                          from_string=lambda x: x in ['True', 'true'],
                          to_string=lambda x: str(x).lower())
Long = Ecore.EDataType('Long', int, 0, from_string=int_conversion)
EJavaObject = Ecore.EDataType('EJavaObject', object)
xmltype = Ecore.EPackage()
xmltype.eClassifiers.extend([String,
                             Double,
                             Int,
                             EJavaObject,
                             Long,
                             Boolean,
                             IntObject])
xmltype.nsURI = 'http://www.eclipse.org/emf/2003/XMLType'
xmltype.nsPrefix = 'xmltype'
xmltype.name = 'xmltype'
rset.metamodel_registry[xmltype.nsURI] = xmltype

# Then the resource can be loaded (here from an http address)
resource = rset.get_resource(HttpURI('http://myadress.ecore'))
root = resource.contents[0]

Metamodel References by ‘File Path’

If a metamodel references others in a ‘file path’ manner (for example, a metamodel A had some relationship towards a B metamodel like this: ../metamodelb.ecore ), PyEcore requires that the B metamodel is loaded first and registered against the metamodel path URI like (in the example, against the ../metamodelb.ecore URI).

>>> # We suppose that the metamodel A.ecore has references towards B.ecore
... # '../../B.ecore'. Path of A.ecore is 'a/b/A.ecore' and B.ecore is '.'
>>> resource = rset.get_resource(URI('B.ecore'))  # We load B.ecore first
>>> root = resource.contents[0]
>>> rset.metamodel_registry['../../B.ecore'] = root  # We register it against the 'file path' uri
>>> resource = rset.get_resource(URI('a/b/A.ecore'))  # A.ecore now loads just fine

Adding External resources

When a model reference another one, they both need to be added inside the same ResourceSet.

rset.get_resource(URI('uri/towards/my/first/resource'))
resource = rset.get_resource(URI('uri/towards/my/secon/resource'))

If for some reason, you want to dynamically create the resource which is required for XMI deserialization of another one, you need to create an empty resource first:

# Other model is 'external_model'
resource = rset.create_resource(URI('the/wanted/uri'))
resource.append(external_model)

Exporting an Existing XMI Resource

As for the XMI import, the XMI export (serialization) is still somehow very basic. Here is an example of how you could save your objects in a file:

>>> # we suppose we have an already existing model in 'root'
>>> from pyecore.resources.xmi import XMIResource
>>> from pyecore.resources import URI
>>> resource = XMIResource(URI('my/path.xmi'))
>>> resource.append(root)  # We add the root to the resource
>>> resource.save()  # will save the result in 'my/path.xmi'
>>> resource.save(output=URI('test/path.xmi'))  # save the result in 'test/path.xmi'

You can also use a ResourceSet to deal with this:

>>> # we suppose we have an already existing model in 'root'
>>> from pyecore.resources import ResourceSet, URI
>>> rset = ResourceSet()
>>> resource = rset.create_resource(URI('my/path.xmi'))
>>> resource.append(root)
>>> resource.save()

Deleting Elements

Deleting elements in EMF is still a sensible point because of all the special model “shape” that can impact the deletion algorithm. PyEcore supports two main way of deleting elements: one is a real kind of deletion, while the other is more less direct.

The delete() method

The first way of deleting element is to use the delete() method which is owned by every EObject/EProxy:

>>> # we suppose we have an already existing element in 'elem'
>>> elem.delete()

This call is also recursive by default: every sub-object of the deleted element is also deleted. This behavior is the one by default as a “containment” reference is a strong constraint.

The behavior of the delete() method can be confusing when there is many EProxy in the game. As the EProxy only gives a partial view of the object while it is not resolved, the delete() can only correctly remove resolved proxies. If a resource or many elements that are referenced in many other resources must be destroyed, in order to be sure to not introduce broken proxies, the best solution is to resolve all the proxies first, then to delete them.

Removing an element from it’s container

You can also, in a way, removing elements from a model using the XMI serialization. If you want to remove an element from a Resource, you have to remove it from its container. PyEcore does not serialize elements that are not contained by a Resource and each reference to this ‘not-contained’ element is not serialized.

Installation

PyEcore is available on pypi, you can simply install it using pip:

$ pip install pyecore

The installation can also be performed manually (better in a virtualenv):

$ python setup.py install

Dependencies

The dependencies required by pyecore are:

• ordered-set which is used for the ordered and unique collections expressed in the metamodel,

• lxml which is used for the XMI parsing.

Run the Tests

Tests uses py.test and ‘coverage’. Everything is driven by Tox, so in order to run the tests simply run:

$ tox

Liberty Regarding the Java EMF Implementation

• There is some meta-property that are not still coded inside PyEcore. More will come with time,

• Resource can only contain a single root at the moment,

• External resources (like http://www.eclipse.org/emf/2003/XMLType) must be create by hand an loaded in the global_registry or as a resource of a ResourceSet,

• Proxies are not “removed” once resolved as in the the Java version, instead they acts as transparent proxies and redirect each calls to the ‘proxied’ object.

State

In the current state, the project implements:

• the dynamic/static metamodel definitions,

• reflexive API,

• inheritance,

• enumerations,

• abstract metaclasses,

• runtime typechecking,

• attribute/reference creations,

• collections (attribute/references with upper bound set to -1),

• reference eopposite,

• containment reference,

• introspection,

• select/reject on collections,

• Eclipse XMI import (partially, only single root models),

• Eclipse XMI export (partially, only single root models),

• simple notification/Event system,

• EOperations support,

• code generator for the static part,

• EMF proxies (first version),

• object deletion (first version).

The things that are in the roadmap:

• URI mapper

• documentation,

• EMF commands (?).

Existing Projects

There is not so much projects proposing to handle model and metamodel in Python. The only projects I found are:

• PyEMOF (http://www.lifl.fr/~marvie/software/pyemof.html)

• EMF4CPP (https://github.com/catedrasaes-umu/emf4cpp)

• PyEMOFUC (http://www.istr.unican.es/pyemofuc/index_En.html)

PyEMOF proposes an implementation of the OMG’s EMOF in Python. The project targets Python2 and supports XMI import/export. The project didn’t move since 2005, but seems quite complete.

EMF4CPP proposes a C++ implementation of EMF. This implementation also introduces Python scripts to call the generated C++ code from a Python environment.

PyEMOFUC proposes, like PyEMOF, a pure Python implementation of the OMG’s EMOF. If we stick to a kind of EMF terminology, PyEMOFUC only supports dynamic metamodels. The project does not seems to move a lot.

Additional Resources

• The article at this address: http://modeling-languages.com/pyecore-python-eclipse-modeling-framework gives more information and implementations details about PyEcore.