As one another approach to plugin system, You may check Extend Me project.
For example, let's define simple class and its extension
# Define base class for extensions (mount point)
class MyCoolClass(Extensible):
my_attr_1 = 25
def my_method1(self, arg1):
print('Hello, %s' % arg1)
# Define extension, which implements some aditional logic
# or modifies existing logic of base class (MyCoolClass)
# Also any extension class maby be placed in any module You like,
# It just needs to be imported at start of app
class MyCoolClassExtension1(MyCoolClass):
def my_method1(self, arg1):
super(MyCoolClassExtension1, self).my_method1(arg1.upper())
def my_method2(self, arg1):
print("Good by, %s" % arg1)
And try to use it:
>>> my_cool_obj = MyCoolClass()
>>> print(my_cool_obj.my_attr_1)
25
>>> my_cool_obj.my_method1('World')
Hello, WORLD
>>> my_cool_obj.my_method2('World')
Good by, World
And show what is hidden behind the scene:
>>> my_cool_obj.__class__.__bases__
[MyCoolClassExtension1, MyCoolClass]
extend_me library manipulates class creation process via metaclasses, thus in example above, when creating new instance of MyCoolClass we got instance of new class that is subclass of both MyCoolClassExtension and MyCoolClass having functionality of both of them, thanks to Python's multiple inheritance
For better control over class creation there are few metaclasses defined in this lib:
ExtensibleType - allows simple extensibility by subclassing
ExtensibleByHashType - similar to ExtensibleType, but haveing ability
to build specialized versions of class, allowing global extension
of base class and extension of specialized versions of class
This lib is used in OpenERP Proxy Project, and seems to be working good enough!
For real example of usage, look in OpenERP Proxy 'field_datetime' extension:
from ..orm.record import Record
import datetime
class RecordDateTime(Record):
""" Provides auto conversion of datetime fields from
string got from server to comparable datetime objects
"""
def _get_field(self, ftype, name):
res = super(RecordDateTime, self)._get_field(ftype, name)
if res and ftype == 'date':
return datetime.datetime.strptime(res, '%Y-%m-%d').date()
elif res and ftype == 'datetime':
return datetime.datetime.strptime(res, '%Y-%m-%d %H:%M:%S')
return res
Record here is extesible object. RecordDateTime is extension.
To enable extension, just import module that contains extension class, and (in case above) all Record objects created after it will have extension class in base classes, thus having all its functionality.
The main advantage of this library is that, code that operates extensible objects, does not need to know about extension and extensions could change everything in extensible objects.
