ConfigurableMeta.py

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# Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
 
# File: AthenaCommon/python/ConfigurableMeta.py
# Author: Wim Lavrijsen (WLavrijsen@lbl.gov)
 
import weakref
from AthenaCommon import Logging, PropertyProxy
 
 

__version__ = '1.2.0'
__author__  = 'Wim Lavrijsen (WLavrijsen@lbl.gov)'
 
__all__ = [ 'ConfigurableMeta' ]
 
 

log = Logging.logging.getLogger( 'ConfigurableMeta' )
 
 

class ConfigurableMeta( type ):
   """The setting of Gaudi component properties needs to be deferred and
      history of who set what where needs to be collected. This is done
      by using PropertyProxy descriptors rather than the default ones."""
 
   def __new__( self, name, bases, dct ):
    # enforce use of classmethod for getType() and setDefaults()
      if 'getType' in dct and not isinstance( dct[ 'getType' ], classmethod ):
         dct[ 'getType' ] = classmethod( dct[ 'getType' ] )
 
      if 'setDefaults' in dct and not isinstance( dct[ 'setDefaults' ], classmethod ):
         dct[ 'setDefaults' ] = classmethod( dct[ 'setDefaults' ] )
 
    # collect what are properties (basically, any public name; C++ variables
    # shouldn't start with an '_' because of portability constraints, hence
    # it is safe to assume that any such vars are python private ones)
      newclass = type.__new__( self, name, bases, dct )
 
      if 'AthenaCommon' not in newclass.__module__:
       # check for required methods and the right number of arguments
       # meths = { 'getServices'   : 1,    # retrieve list of services to configure
         meths = { 'getDlls'       : 1,    # provide list of Dlls to load
                   'getGaudiType'  : 1,    # return string describing component class
                   'getHandle'     : 1,    # provide access to C++ side component instance
                   'getType'       : 1 }   # return the type of the actual C++ component
 
         for meth, nArgs in meths.items():
            try:
               f = getattr( newclass, meth )
            except AttributeError:
               raise NotImplementedError("%s is missing in class %s" % (meth,str(newclass)))
 
          # in addition, verify the number of arguments w/o defaults
            nargcount = f.__code__.co_argcount
            dflts = f.__defaults__
            ndefaults = dflts and len(dflts) or 0
            if not nargcount - ndefaults <= nArgs <= nargcount:
               raise TypeError("%s.%s requires exactly %d arguments" % (newclass,meth,nArgs))
 
    # cache references of instances by name for duplicate removal
      newclass.configurables = weakref.WeakValueDictionary()
 
    # loop over slots, which are all assumed to be properties, create proxies, defaults
      properties = {}
      slots = dct.get( '__slots__' )
      if slots:
         props = [ x for x in slots if x[0] != '_' ]
         propDict = dct.get('_propertyDocDct')
         for prop in props:
            docString = propDict and propDict.get(prop)
            if type(slots) is dict:
               default = slots[prop]
            else:
               default = None
            proxy = PropertyProxy.PropertyProxyFactory(
               getattr( newclass, prop ), docString, default )
 
            properties[ prop ] = proxy
            setattr( newclass, prop, proxy )
 
    # complete set of properties includes those from base classes
      for base in bases:
         try:
            bprops = base._properties.copy()
            bprops.update( properties )
            properties = bprops
         except AttributeError:
            pass
 
      newclass._properties = properties
 
      return newclass
 
   def __call__( cls, *args, **kwargs ):
      """To Gaudi, any object with the same type/name is the same object. Hence,
         this is mimicked in the configuration: instantiating a new Configurable
         of a type with the same name will return the same instance."""
 
    # Get the instance: `singleton' logic needs to be in __new__, not here,
    # for compatibililty with pickling.)
      cfg = cls.__new__( cls, *args, **kwargs )
 
    # Initialize the object, if not done already.
      if cfg and ( not hasattr(cfg, '_fInitOk') or not cfg._fInitOk ):
         cls.__init__( cfg, *args, **kwargs )
 
      return cfg