class lsst.pipe.base.Struct(**keyArgs: Any)

Bases: SimpleNamespace

A container to which you can add fields as attributes.


keyword arguments specifying fields and their values.


Intended to be used for the return value from run and other Task methods, and useful for any method that returns multiple values.

The intent is to allow accessing returned items by name, instead of unpacking a tuple. This makes the code much more robust and easier to read. It allows one to change what values are returned without inducing mysterious failures: adding items is completely safe, and removing or renaming items causes errors that are caught quickly and reported in a way that is easy to understand.

The primary reason for using Struct instead of dict is that the fields may be accessed as attributes, e.g. instead of aDict["foo"]. Admittedly this only saves a few characters, but it makes the code significantly more readable.

Struct is preferred over named tuples, because named tuples can be used as ordinary tuples, thus losing all the safety advantages of Struct. In addition, named tuples are clumsy to define and Structs are much more mutable (e.g. one can trivially combine Structs and add additional fields).


>>> myStruct = Struct(
>>>     strVal = 'the value of the field named "strVal"',
>>>     intVal = 35,
>>> )

Methods Summary


Make a one-level-deep copy (values are not copied).


Get a dictionary of fields in this struct.

mergeItems(struct, *nameList)

Copy specified fields from another struct, provided they don't already exist.

Methods Documentation

copy() Struct

Make a one-level-deep copy (values are not copied).


One-level-deep copy of this Struct.

getDict() dict[str, Any]

Get a dictionary of fields in this struct.


Dictionary with field names as keys and field values as values. The values are shallow copies.

mergeItems(struct: Struct, *nameList: str) None

Copy specified fields from another struct, provided they don’t already exist.


Struct from which to copy.


All remaining arguments are names of items to copy.


Raised if any item in nameList already exists in self (but any items before the conflicting item in nameList will have been copied).


For example:

foo.copyItems(other, "itemName1", "itemName2")

copies other.itemName1 and other.itemName2 into self.