The configuration of analysis algorithm sequences is somewhat more complicated than regular algorithm sequences, basically because the configuration of individual algorithms isn’t independent, but instead later algorithms depend on the configuration of algorithms earlier in the sequence.
The way it works is that each algorithm in the sequence has some
meta-configuration associated with it, and then in a
post-configuration step the meta-configuration gets converted into
actual property values. If you followed the beginners tutorial that
is what the
algSeq.configure(...) call does. For more details on
the post-configuration see the beginner’s tutorial, the rest of this
page focuses on the meta-configuration.
The reason for attaching the meta-configuration to the sequence instead of setting the properties directly is that it allows to manipulate the sequence after it has been assembled (but before the post-configuration), e.g. algorithms can be added, removed or reordered.
You can get a better feel of how this works by looking at some existing examples, e.g.: https://gitlab.cern.ch/atlas/athena/-/blob/21.2/PhysicsAnalysis/Algorithms/MuonAnalysisAlgorithms/python/MuonAnalysisSequence.py https://gitlab.cern.ch/atlas/athena/-/blob/21.2/PhysicsAnalysis/Algorithms/JetAnalysisAlgorithms/python/JetAnalysisSequence.py https://gitlab.cern.ch/atlas/athena/-/blob/21.2/PhysicsAnalysis/Algorithms/MetAnalysisAlgorithms/python/MetAnalysisSequence.py
One of the basic ideas of configuring analysis sequences is that
usually the whole sequence works with one object type (e.g. muons) and
the output of each algorithm is used as input for the next algorithm.
To that end, the name of the property holding the input container is
inputPropName and the name of the property holding the
output container is
This generally matches nicely with the
SysCopyHandle that most CP
algorithms use internally, which has both a property for the input
container and the output container. It should be noted though that
outputPropName can be omitted if the algorithm shouldn’t
make a copy internally (or if it doesn’t use a copy handle).
Some algorithms like (MET and overlap removal) have multiple inputs/outputs, in which case these meta-properties are configured using a dictionary instead of a single string.
Some important caveats:
SysListLoaderAlg), but is a filter on the list of systematics. So if the user decides not to run a systematics it can just be omitted in
SysListLoaderAlgwithout any changes here.
There are some properties (like
preselection) that are not involved
in systematics handling but will still depend on what algorithms came
in the sequence before the algorithm in question. In the past we
would just have had a python variable we maintain as we configure the
algorithm sequence. And while that worked fine as long as you used
the sequence as is, it made it very hard to add/remove/reorder
So the idea is that instead of tracking these properties in a python
variable we add meta-information to the algorithm sequence and then
create the actual property value during post-configuration. In more
practical terms, you use
metaConfig to set the configuration values
that you want to communicate to subsequent algorithms, and then
dynConfig to declare the actual property to set. You can also add
default/starting values to the entire sequence via
Three of the finer points:
dynConfiguses a lambda function to convert the list of values into the property value.