ConfigAccumulator.py

Go to the documentation of this file.

# Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration
 
import AnaAlgorithm.DualUseConfig as DualUseConfig
from AthenaConfiguration.Enums import LHCPeriod, FlagEnum
import re
 
import warnings
import functools
 
# warn about deprecations with a FutureWarning instead of a
# DeprecationWarning, because DeprecatedWarning is not shown by default
deprecationWarningCategory = FutureWarning
def deprecated(reason: str = ""):
    def decorator(func):
        message = f"{func.__qualname__} is deprecated."
        if reason:
            message += " " + reason
 
        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            warnings.warn(
                message,
                category=deprecationWarningCategory,
                stacklevel=2,
            )
            return func(*args, **kwargs)
 
        return wrapper
    return decorator
 
class ExpertModeWarning(Warning):
    """Warning raised when an expert-only configuration option is used."""
    pass
# Default filter: error out unless the user overrides
if not any(f[0] == 'error' and f[2] is ExpertModeWarning for f in warnings.filters):
    warnings.simplefilter('error', ExpertModeWarning)
 
class DataType(FlagEnum):
    """holds the various data types as an enum"""
    Data = 'data'
    FullSim = 'fullsim'
    FastSim = 'fastsim'
 
 
class SelectionConfig :
    """all the data for a given selection that has been registered
 
    the bits argument is for backward compatibility, does nothing, and will be
    removed in the future."""
 
    def __init__ (self, selectionName, decoration,
                  *, bits=0, preselection=None, comesFrom = '',
                  writeToOutput=True) :
        self.name = selectionName
        self.decoration = decoration
        if preselection is not None :
            self.preselection = preselection
        else :
            self.preselection = (selectionName == '')
        self.comesFrom = comesFrom
        self.writeToOutput = writeToOutput
 
 
 
class OutputConfig :
    """all the data for a given variables in the output that has been registered"""
 
    def __init__ (self, origContainerName, variableName,
                  *, noSys, enabled, auxType) :
        self.origContainerName = origContainerName
        self.outputContainerName = None
        self.variableName = variableName
        self.noSys = noSys
        self.enabled = enabled
        self.auxType = auxType
 
    def __repr__ (self):
        return f'OutputConfig("{self.outputContainerName}.{self.variableName}" [enabled={self.enabled}])'
 
class ContainerConfig :
    """all the auto-generated meta-configuration data for a single container
 
    This tracks the naming of all temporary containers, as well as all the
    selection decorations."""
 
    def __init__ (self, name, sourceName, *, originalName = None, isMet = False, noSysSuffix) :
        self.name = name
        self.sourceName = sourceName
        self.originalName = originalName
        self.noSysSuffix = noSysSuffix
        self.index = 0
        self.maxIndex = None
        self.viewIndex = 1
        self.isMet = isMet
        self.selections = []
        self.outputs = {}
        self.meta = {}
 
    def currentName (self, *, nominal=False) :
        if self.index == 0 :
            if self.sourceName is None :
                raise Exception ("should not get here, reading container name before created: " + self.name)
            return self.sourceName
        if self.maxIndex and self.index == self.maxIndex :
            result = self.systematicsName(self.name, noSysSuffix=self.noSysSuffix)
        else :
            result = self.systematicsName(f"{self.name}_STEP{self.index}", noSysSuffix=self.noSysSuffix)
        if nominal :
             result = result.replace("%SYS%", "NOSYS")
        return result
 
    @staticmethod
    def systematicsName (name, *, noSysSuffix) :
        """map an internal name to a name for systematics data handles
 
        Right now this just means appending a _%SYS% to the name."""
        if not noSysSuffix :
            return name + "_%SYS%"
        else :
            return name
 
    def nextPass (self) :
        self.maxIndex = self.index
        self.index = 0
        self.viewIndex = 1
        self.selections = []
        self.outputs = {}
        self.meta = {}
 
 
 
class ConfigAccumulator :
    """a class that accumulates a configuration from blocks into an
    algorithm sequence
 
    This is used as argument to the ConfigurationBlock methods, which
    need to be called in the correct order.  This class will track all
    meta-information that needs to be communicated between blocks
    during configuration, and also add the created algorithms to the
    sequence.
 
    Use/access of containers in the event store is handled via
    references that this class hands out.  This happens in a separate
    step before the algorithms are created, as the naming of
    containers will depend on where in the chain the container is
    used.
 
    All arguments passed to the ConfigAccumulator constructor are used
    as they are. The only exception is the systematics flag:
    If not explicitly set the decision to run systematics or not
    will be taken depending on the CommonServicesConfig setup.
    """
 
    def __init__ (self, *, flags=None, algSeq=None, noSysSuffix=False, noSystematics=None, dataType=None, isPhyslite=None, geometry=None, dsid=0, campaign=None, runNumber=None, autoconfigFromFlags=None, dataYear=0):
 
        # Historically we have used the identifier
        # `autoconfigFromFlags`, but in the rest of the code base
        # `flags` is used. So for now we allow either, and can hopefully
        # at some point remove the former (21 Aug 25).
        if autoconfigFromFlags is not None:
            if flags is not None:
                raise ValueError("Cannot pass both flags and autoconfigFromFlags arguments")
            flags = autoconfigFromFlags
            warnings.warn ('Using autoconfigFromFlags parameter is deprecated, use flags instead', category=deprecationWarningCategory, stacklevel=2)
        self._flags = flags
 
        # Historically the user was expected to pass in meta-data
        # manually, which was a complete underestimate of the amount of
        # meta-data needed. The current recommendation is to pass in a
        # configuration flags object instead. The code below will raise
        # an error if both are done, and if no configuration flags are
        # passed in, it will try to create a flags object from the
        # passed in parameters.
        if self._flags is not None:
            if dataType is not None:
                raise ValueError("Cannot pass both dataType and flags/autoconfigFromFlags arguments")
            if isPhyslite is not None:
                raise ValueError("Cannot pass both isPhyslite and flags/autoconfigFromFlags arguments")
            if geometry is not None:
                raise ValueError("Cannot pass both geometry and flags/autoconfigFromFlags arguments")
            if dsid != 0:
                raise ValueError("Cannot pass both dsid and flags/autoconfigFromFlags arguments")
            if campaign is not None:
                raise ValueError("Cannot pass both campaign and flags/autoconfigFromFlags arguments")
            if runNumber is not None:
                raise ValueError("Cannot pass both runNumber and flags/autoconfigFromFlags arguments")
            if dataYear != 0:
                raise ValueError("Cannot pass both dataYear and flags/autoconfigFromFlags arguments")
 
            if self._flags.Input.isMC:
                if self._flags.Sim.ISF.Simulator.usesFastCaloSim():
                    dataType = DataType.FastSim
                else:
                    dataType = DataType.FullSim
            else:
                dataType = DataType.Data
            isPhyslite = 'StreamDAOD_PHYSLITE' in self._flags.Input.ProcessingTags
            from TrigDecisionTool.TrigDecisionToolHelpers import (
                getRun3NavigationContainerFromInput_forAnalysisBase)
            hltSummary = getRun3NavigationContainerFromInput_forAnalysisBase(self._flags)
        else:
            warnings.warn ('it is deprecated to configure meta-data for analysis configuration manually, please read the configuration flags via the meta-data reader', category=deprecationWarningCategory, stacklevel=2)
            from AthenaConfiguration.AllConfigFlags import initConfigFlags
            flags = initConfigFlags()
            if dataType is None:
                raise ValueError ("need to specify dataType if flags are not set")
            # legacy mappings of string arguments
            if isinstance(dataType, str):
                if dataType == 'mc':
                    dataType = DataType.FullSim
                elif dataType == 'afii':
                    dataType = DataType.FastSim
                else:
                    dataType = DataType(dataType)
            if isPhyslite is None:
                isPhyslite = False
            if geometry is not None:
                # allow possible string argument for `geometry` and convert it to enum
                geometry = LHCPeriod(geometry)
                if geometry is LHCPeriod.Run1:
                    raise ValueError ("invalid Run geometry: %s" % geometry.value)
                flags.GeoModel.Run = geometry
            if dsid != 0:
                flags.Input.MCChannelNumber = dsid
            if campaign is not None:
                flags.Input.MCCampaign = campaign
            if dataYear != 0:
                flags.Input.DataYear = dataYear
            if runNumber is None:
                # not sure if we should just use a default run number
                # here, or just report nothing
                runNumber = 284500
            flags.Input.RunNumbers = [runNumber]
            hltSummary = 'HLTNav_Summary_DAODSlimmed'
            flags.lock()
            self._flags = flags
 
        # These don't seem to have a direct equivalent in the
        # configuration flags. For now I'm keeping them (21 Aug 25), but
        # they might be replaced with something that is more directly in
        # the configuration flags in the future.
        self._dataType = dataType
        self._isPhyslite = isPhyslite
        self._hltSummary = hltSummary
 
        # From here on, we are no longer dealing with flags or
        # meta-data, but actual internal variables we need to manage the
        # creation of components.
        self._algSeq = algSeq
        self._noSystematics = noSystematics
        self._noSysSuffix = noSysSuffix
        self._algPostfix = ''
        self._defaultHistogramStream = 'ANALYSIS'
        self._containerConfig = {}
        self._outputContainers = {}
        self._pass = 0
        self._algorithms = {}
        self._currentAlg = None
        self._selectionNameExpr = re.compile ('[A-Za-z_][A-Za-z_0-9]+')
        self.setSourceName ('EventInfo', 'EventInfo')
        self._eventcutflow = {}
        self.CA = None
 
        if DualUseConfig.isAthena:
            from AthenaConfiguration.ComponentAccumulator import ComponentAccumulator
            self.CA = ComponentAccumulator()
            if algSeq is not None:
                self.CA.addSequence(algSeq)
        else:
            if algSeq is None :
                raise ValueError ("need to pass algSeq if not using ComponentAccumulator")
 
    def noSystematics (self) :
        """noSystematics flag used by CommonServices block"""
        return self._noSystematics
 
    @property
    def flags (self) :
        """Athena configuration flags"""
        return self._flags
 
    @deprecated("use the flags property instead")
    def autoconfigFlags (self) :
        """Athena configuration flags
        
        This is a backward compatibility version of the flags property,
        which is preferred."""
        return self._flags
 
    def dataType (self) :
        """the data type we run on (data, fullsim, fastsim)"""
        return self._dataType
 
    def isPhyslite (self) :
        """whether we run on PHYSLITE"""
        return self._isPhyslite
 
    def geometry (self) :
        """the LHC Run period we run on"""
        return self._flags.GeoModel.Run
 
    def dsid(self) :
        """the mcChannelNumber or DSID of the sample we run on"""
        return self._flags.Input.MCChannelNumber
 
    def campaign(self) :
        """the MC campaign we run on"""
        return self._flags.Input.MCCampaign
 
    def runNumber(self) :
        """the MC runNumber"""
        return int(self._flags.Input.RunNumbers[0])
 
    def dataYear(self) :
        """for data, the corresponding year; for MC, zero"""
        return self._flags.Input.DataYear
 
    def generatorInfo(self) :
        """the dictionary of MC generators and their versions for the sample we run on"""
        return self._flags.Input.GeneratorsInfo
 
    def hltSummary(self) :
        """the HLTSummary configuration to be used for the trigger decision tool"""
        return self._hltSummary
 
    def defaultHistogramStream(self):
        """the default histogram stream to be used for output histograms"""
        return self._defaultHistogramStream
 
    def setDefaultHistogramStream(self, streamName: str):
        """set the default histogram stream to be used for output histograms
        
        As an advanced option this is not directly exposed by the constructor,
        but can be set by the user if needed before configuring the job."""
        self._defaultHistogramStream = streamName
    
    def algPostfix (self) :
        """the current postfix to be appended to algorithm names
        
        Blocks should not call this directly, but rather implement the
        instanceName method, which will be used to generate the postfix
        automatically."""
        return self._algPostfix
    
    def setAlgPostfix (self, postfix : str) :
        """set the current postfix to be appended to algorithm names
 
        Blocks should not call this directly, but rather implement the
        instanceName method, which will be used to generate the postfix
        automatically."""
        # make sure the postfix matches the expected format ([_a-zA-Z0-9]*)
        if re.compile ('^[_a-zA-Z0-9]*$').match (postfix) is None :
            raise ValueError ('invalid algorithm postfix: ' + postfix)
        if postfix == '' :
            self._algPostfix = ''
        elif postfix[0] != '_' :
            self._algPostfix = '_' + postfix
        else :
            self._algPostfix = postfix
 
    def getAlgorithm (self, name : str):
        """get the algorithm with the given name
        
        Despite the name this will also return services and tools. It is
        mostly meant for internal use, particularly for the property
        overrides."""
        name = name + self._algPostfix
        if name not in self._algorithms:
            return None
        return self._algorithms[name]
 
    def createAlgorithm (self, type, name, reentrant=False) :
        """create a new algorithm and register it as the current algorithm"""
        name = name + self._algPostfix
        if self._pass == 0 :
            if name in self._algorithms :
                raise Exception ('duplicate algorithms: ' + name + ' with algPostfix=' + self._algPostfix)
            if reentrant:
                alg = DualUseConfig.createReentrantAlgorithm (type, name)
            else:
                alg = DualUseConfig.createAlgorithm (type, name)
 
            if DualUseConfig.isAthena:
                if self._algSeq is not None:
                    self.CA.addEventAlgo(alg,self._algSeq.name)
                else :
                    self.CA.addEventAlgo(alg)
            else:
                self._algSeq += alg
 
            self._algorithms[name] = alg
            self._currentAlg = alg
            return alg
        else :
            if name not in self._algorithms :
                raise Exception ('unknown algorithm requested: ' + name)
            self._currentAlg = self._algorithms[name]
            if self.CA and self._currentAlg != self.CA.getEventAlgo(name) :
                raise Exception ('change to algorithm object: ' + name)
            return self._algorithms[name]
 
 
    def createService (self, type, name) :
        '''create a new service and register it as the "current algorithm"'''
        if self._pass == 0 :
            if name in self._algorithms :
                raise Exception ('duplicate service: ' + name)
            service = DualUseConfig.createService (type, name)
            # Avoid importing AthenaCommon.AppMgr in a CA Athena job
            # as it modifies Gaudi behaviour
            if DualUseConfig.isAthena:
                self.CA.addService(service)
            else:
                # We're not, so let's remember this as a "normal" algorithm:
                self._algSeq += service
            self._algorithms[name] = service
            self._currentAlg = service
            return service
        else :
            if name not in self._algorithms :
                raise Exception ('unknown service requested: ' + name)
            self._currentAlg = self._algorithms[name]
            return self._algorithms[name]
 
 
    def createPublicTool (self, type, name) :
        '''create a new public tool and register it as the "current algorithm"'''
        if self._pass == 0 :
            if name in self._algorithms :
                raise Exception ('duplicate public tool: ' + name)
            tool = DualUseConfig.createPublicTool (type, name)
            # Avoid importing AthenaCommon.AppMgr in a CA Athena job
            # as it modifies Gaudi behaviour
            if DualUseConfig.isAthena:
                self.CA.addPublicTool(tool)
            else:
                # We're not, so let's remember this as a "normal" algorithm:
                self._algSeq += tool
            self._algorithms[name] = tool
            self._currentAlg = tool
            return tool
        else :
            if name not in self._algorithms :
                raise Exception ('unknown public tool requested: ' + name)
            self._currentAlg = self._algorithms[name]
            return self._algorithms[name]
 
 
    def addPrivateTool (self, propertyName, toolType) :
        """add a private tool to the current algorithm"""
        if self._pass == 0 :
            DualUseConfig.addPrivateTool (self._currentAlg, propertyName, toolType)
 
    def setExtraInputs (self, inputs) :
        """set extra input dependencies for the current algorithm"""
        if DualUseConfig.isAthena:
            self._currentAlg.ExtraInputs = inputs
 
    def setExtraOutputs (self, outputs) :
        """set extra output dependencies for the current algorithm"""
        if DualUseConfig.isAthena:
            self._currentAlg.ExtraOutputs = outputs
 
    def setSourceName (self, containerName, sourceName,
                       *, originalName = None, isMet = False) :
        """set the (default) name of the source/original container
 
        This is essentially meant to allow using e.g. the muon
        configuration and the user not having to manually specify that
        they want to use the Muons/AnalysisMuons container from the
        input file.
 
        In addition it allows to set the original name of the
        container (which may be different from the source name), which
        is mostly/exclusively used for jet containers, so that
        subsequent configurations know which jet container they
        operate on.
        """
        if containerName not in self._containerConfig :
            self._containerConfig[containerName] = ContainerConfig (containerName, sourceName, noSysSuffix = self._noSysSuffix, originalName = originalName, isMet = isMet)
 
 
    def writeName (self, containerName, *, isMet=None) :
        """register that the given container will be made and return
        its name"""
        if containerName not in self._containerConfig :
            self._containerConfig[containerName] = ContainerConfig (containerName, sourceName = None, noSysSuffix = self._noSysSuffix)
        if self._containerConfig[containerName].sourceName is not None :
            raise Exception ("trying to write container configured for input: " + containerName)
        if self._containerConfig[containerName].index != 0 :
            raise Exception ("trying to write container twice: " + containerName)
        self._containerConfig[containerName].index += 1
        if isMet is not None :
            self._containerConfig[containerName].isMet = isMet
        return self._containerConfig[containerName].currentName()
 
 
    def readName (self, containerName, *, nominal=False) :
        """get the name of the "current copy" of the given container
 
        As extra copies get created during processing this will track
        the correct name of the current copy.  Optionally one can pass
        in the name of the container before the first copy.
        """
        if containerName not in self._containerConfig :
            raise Exception ("no source container for: " + containerName)
        return self._containerConfig[containerName].currentName(nominal=nominal)
 
 
    def copyName (self, containerName) :
        """register that a copy of the container will be made and return
        its name"""
        if containerName not in self._containerConfig :
            raise Exception ("unknown container: " + containerName)
        self._containerConfig[containerName].index += 1
        return self._containerConfig[containerName].currentName()
 
 
    def wantCopy (self, containerName) :
        """ask whether we want/need a copy of the container
 
        This usually only happens if no copy of the container has been
        made yet and the copy is needed to allow modifications, etc.
        """
        if containerName not in self._containerConfig :
            raise Exception ("no source container for: " + containerName)
        return self._containerConfig[containerName].index == 0
 
 
    def originalName (self, containerName) :
        """get the "original" name of the given container
 
        This is mostly/exclusively used for jet containers, so that
        subsequent configurations know which jet container they
        operate on.
        """
        if containerName not in self._containerConfig :
            raise Exception ("container unknown: " + containerName)
        result = self._containerConfig[containerName].originalName
        if result is None :
            raise Exception ("no original name for: " + containerName)
        return result
 
    def getContainerMeta (self, containerName, metaField, defaultValue=None, *, failOnMiss=False) :
        """get the meta information for the given container
 
        This is used to pass down meta-information from the
        configuration to the algorithms.
        """
        if containerName not in self._containerConfig :
            raise Exception ("container unknown: " + containerName)
        if metaField in self._containerConfig[containerName].meta :
            return self._containerConfig[containerName].meta[metaField]
        if failOnMiss :
            raise Exception ('unknown meta-field' + metaField + ' on container ' + containerName)
        return defaultValue
 
    def setContainerMeta (self, containerName, metaField, value, *, allowOverwrite=False) :
        """set the meta information for the given container
 
        This is used to pass down meta-information from the
        configuration to the algorithms.
        """
        if containerName not in self._containerConfig :
            raise Exception ("container unknown: " + containerName)
        if not allowOverwrite and metaField in self._containerConfig[containerName].meta :
            raise Exception ('duplicate meta-field' + metaField + ' on container ' + containerName)
        self._containerConfig[containerName].meta[metaField] = value
 
    def isMetContainer (self, containerName) :
        """whether the given container is registered as a MET container
 
        This is mostly/exclusively used for determining whether to
        write out the whole container or just a single MET term.
        """
        if containerName not in self._containerConfig :
            raise Exception ("container unknown: " + containerName)
        return self._containerConfig[containerName].isMet
 
 
    def readNameAndSelection (self, containerName, *, excludeFrom = None) :
        """get the name of the "current copy" of the given container, and the
        selection string
 
        This is mostly meant for MET and OR for whom the actual object
        selection is relevant, and which as such allow to pass in the
        working point as "ObjectName.WorkingPoint".
        """
        split = containerName.split (".")
        if len(split) == 1 :
            objectName = split[0]
            selectionName = ''
        elif len(split) == 2 :
            objectName = split[0]
            selectionName = split[1]
        else :
            raise Exception ('invalid object selection name: ' + containerName)
        return self.readName (objectName), self.getFullSelection (objectName, selectionName, excludeFrom=excludeFrom)
 
 
    def nextPass (self) :
        """switch to the next configuration pass
 
        Configuration happens in two steps, with all the blocks processed
        twice.  This switches from the first to the second pass.
        """
        if self._pass != 0 :
            raise Exception ("already performed final pass")
        for name in self._containerConfig :
            self._containerConfig[name].nextPass ()
        self._pass = 1
        self._currentAlg = None
        self._outputContainers = {}
 
 
    def getPreselection (self, containerName, selectionName, *, asList = False) :
 
        """get the preselection string for the given selection on the given
        container
        """
        if selectionName != '' and not self._selectionNameExpr.fullmatch (selectionName) :
            raise ValueError ('invalid selection name: ' + selectionName)
        if containerName not in self._containerConfig :
            return ""
        config = self._containerConfig[containerName]
        decorations = []
        for selection in config.selections :
            if (selection.name == '' or selection.name == selectionName) and \
               selection.preselection :
                decorations += [selection.decoration]
        if asList :
            return decorations
        else :
            return '&&'.join (decorations)
 
 
    def getFullSelection (self, containerName, selectionName,
                          *, skipBase = False, excludeFrom = None) :
 
        """get the selection string for the given selection on the given
        container
 
        This can handle both individual selections or selection
        expressions (e.g. `loose||tight`) with the later being
        properly expanded.  Either way the base selection (i.e. the
        selection without a name) will always be applied on top.
 
        containerName --- the container the selection is defined on
        selectionName --- the name of the selection, or a selection
                          expression based on multiple named selections
        skipBase --- will avoid the base selection, and should normally
                     not be used by the end-user.
        excludeFrom --- a set of string names of selection sources to exclude
                        e.g. to exclude OR selections from MET
        """
        if "." in containerName:
            raise ValueError (f'invalid containerName argument: {containerName} , it contains a "." '
            'which is used to indicate container+selection. You should only pass the container.')
        if containerName not in self._containerConfig :
            return ""
 
        if excludeFrom is None :
            excludeFrom = set()
        elif not isinstance(excludeFrom, set) :
            raise ValueError ('invalid excludeFrom argument (need set of strings): ' + str(excludeFrom))
 
        # Check if this is actually a selection expression,
        # e.g. `A||B` and if so translate it into a complex expression
        # for the user.  I'm not trying to do any complex syntax
        # recognition, but instead just produce an expression that the
        # C++ parser ought to be able to read.
        if selectionName != '' and \
           not self._selectionNameExpr.fullmatch (selectionName) :
            result = ''
            while selectionName != '' :
                match = self._selectionNameExpr.match (selectionName)
                if not match :
                    result += selectionName[0]
                    selectionName = selectionName[1:]
                else :
                    subname = match.group(0)
                    subresult = self.getFullSelection (containerName, subname, skipBase = True, excludeFrom=excludeFrom)
                    if subresult != '' :
                        result += '(' + subresult + ')'
                    else :
                        result += 'true'
                    selectionName = selectionName[len(subname):]
            subresult = self.getFullSelection (containerName, '', excludeFrom=excludeFrom)
            if subresult != '' :
                result = subresult + '&&(' + result + ')'
            return '(' + result + ')' if result !='' else ''
 
        config = self._containerConfig[containerName]
        decorations = []
        hasSelectionName = False
        for selection in config.selections :
            if ((selection.name == '' and not skipBase) or selection.name == selectionName) and (selection.comesFrom not in excludeFrom) :
                decorations += [selection.decoration]
            if selection.name == selectionName :
                hasSelectionName = True
        if not hasSelectionName and selectionName != '' :
            raise KeyError ('invalid selection name: ' + containerName + '.' + selectionName)
        return '&&'.join (decorations)
 
 
    def getSelectionCutFlow (self, containerName, selectionName) :
 
        """get the individual selections as a list for producing the cutflow for
        the given selection on the given container
 
        This can only handle individual selections, not selection
        expressions (e.g. `loose||tight`).
 
        """
        if containerName not in self._containerConfig :
            return []
 
        # Check if this is actually a selection expression,
        # e.g. `A||B` and if so translate it into a complex expression
        # for the user.  I'm not trying to do any complex syntax
        # recognition, but instead just produce an expression that the
        # C++ parser ought to be able to read.
        if selectionName != '' and \
           not self._selectionNameExpr.fullmatch (selectionName) :
            raise ValueError ('not allowed to do cutflow on selection expression: ' + selectionName)
 
        config = self._containerConfig[containerName]
        decorations = []
        for selection in config.selections :
            if (selection.name == '' or selection.name == selectionName) :
                decorations += [selection.decoration]
        return decorations
 
 
    def addEventCutFlow (self, selection, decorations) :
 
        """register a new event cutflow, adding it to the dictionary with key 'selection'
        and value 'decorations', a list of decorated selections
        """
        if self._pass == 0:
            if selection in self._eventcutflow.keys():
                raise ValueError ('the event cutflow dictionary already contains an entry ' + selection)
            else:
                self._eventcutflow[selection] = decorations
 
 
    def getEventCutFlow (self, selection) :
 
        """get the list of decorated selections for an event cutflow,  corresponding to
        key 'selection'
        """
        return self._eventcutflow[selection]
 
 
    def addSelection (self, containerName, selectionName, decoration,
                      **kwargs) :
        """add another selection decoration to the selection of the given
        name for the given container"""
        if selectionName != '' and not self._selectionNameExpr.fullmatch (selectionName) :
            raise ValueError ('invalid selection name: ' + selectionName)
        if containerName not in self._containerConfig :
            self._containerConfig[containerName] = ContainerConfig (containerName, containerName, noSysSuffix=self._noSysSuffix)
        config = self._containerConfig[containerName]
        selection = SelectionConfig (selectionName, decoration, **kwargs)
        config.selections.append (selection)
 
 
    def addOutputContainer (self, containerName, outputContainerName) :
        """register a copy of a container used in outputs"""
        if containerName not in self._containerConfig :
            raise KeyError ("container unknown: " + containerName)
        if outputContainerName in self._outputContainers :
            raise KeyError ("duplicate output container name: " + outputContainerName)
        self._outputContainers[outputContainerName] = containerName
 
 
    def checkOutputContainer (self, containerName) :
        """check whether a given container has been registered in outputs"""
        return containerName in self._outputContainers.values()
 
 
    def getOutputContainerOrigin (self, outputContainerName) :
        """Get the name of the actual container, for which an output is registered"""
        try:
            return self._outputContainers[outputContainerName]
        except KeyError:
            try:
                return self._containerConfig[outputContainerName].name
            except KeyError:
                raise KeyError ("output container unknown: " + outputContainerName)
 
 
    def addOutputVar (self, containerName, variableName, outputName,
                      *, noSys=False, enabled=True, auxType=None) :
        """add an output variable for the given container to the output
        """
 
        if containerName not in self._containerConfig :
            raise KeyError ("container unknown: " + containerName)
        baseConfig = self._containerConfig[containerName].outputs
        if outputName in baseConfig :
            raise KeyError ("duplicate output variable name: " + outputName)
        config = OutputConfig (containerName, variableName, noSys=noSys, enabled=enabled, auxType=auxType)
        baseConfig[outputName] = config
 
 
    def getOutputVars (self, containerName) :
        """get the output variables for the given container"""
        if containerName in self._outputContainers :
            containerName = self._outputContainers[containerName]
        if containerName not in self._containerConfig :
            raise KeyError ("unknown container for output: " + containerName)
        return self._containerConfig[containerName].outputs
 
 
    def getSelectionNames (self, containerName, excludeFrom = None) :
        """Retrieve set of unique selections defined for a given container"""
        if containerName not in self._containerConfig :
            return []
        if excludeFrom is None:
            excludeFrom = set()
        elif not isinstance(excludeFrom, set) :
            raise ValueError ('invalid excludeFrom argument (need set of strings): ' + str(excludeFrom))
 
        config = self._containerConfig[containerName]
        # because cuts are registered individually, selection names can repeat themselves
        # but we are interested in unique names only
        selectionNames = set()
        for selection in config.selections:
            if selection.comesFrom in excludeFrom:
                continue
            # skip flags which should be disabled in output
            if selection.writeToOutput:
                selectionNames.add(selection.name)
        return selectionNames