IO (Python)

The IO Cython class wraps the C++ ROOT/HDF5 I/O engine. It iterates over events stored in ROOT TTree files and exposes them as dictionaries of data_t objects keyed by leaf name.

Constructor

IO(root=[]) — pass a list of ROOT file paths to open immediately.

Iteration Protocol

IO implements Python’s iterator protocol. Each next() call returns a dictionary:

reader = IO()
reader.Trees   = ["nominal"]
reader.Branches = ["jet_pt", "jet_eta"]
reader.ScanKeys()
reader.begin()
for event in reader:
    jet_pt = event[b"nominal.jet_pt.jet_pt"]

Methods

Signature	Description
`ScanKeys()`	Scan the registered files and build the internal key map. Must be called before iterating.
`begin()`	Rewind the internal cursor to the first event.
`end()`	Release internal file handles and free memory.
`MetaData() → dict[str, Meta]`	Return a dictionary of `Meta` objects (ATLAS dataset metadata) keyed by dataset label.

Properties

Property	Type	Description
`Verbose`	`bool`	Enable/disable console progress output.
`EnablePyAMI`	`bool`	If `True`, query the ATLAS AMI database for metadata.
`MetaCachePath`	`str`	Directory where AMI metadata cache JSON files are stored.
`SumOfWeightsTreeName`	`str`	Name of the ROOT tree that stores sum-of-weights information.
`Trees`	`list[str]`	TTree names to read.
`Branches`	`list[str]`	TBranch names to read.
`Leaves`	`list[str]`	Registered leaf names (read-only; populated by `ScanKeys`).
`Files`	`list[str]`	List of ROOT file paths to process.
`Keys`	`dict`	Nested dictionary `{file: {tree: {branch: [leaves]}}}`.