NonemptyMapping

class lsst.daf.butler.nonempty_mapping.NonemptyMapping(default_factory: Callable[[], _V])

Bases: Mapping[_K, _V]

A Mapping that implicitly adds values (like defaultdict) but treats any that evaluate to False as not present.

Parameters:

default_factoryCallable

A callable that takes no arguments and returns a new instance of the value type.

Notes

Unlike defaultdict, this class implements only collections.abc.Mapping, not MutableMapping, and hence it can be modified only by invoking __getitem__ with a key that does not exist. It is expected that the value type will be a mutable container like set or dict, and that an empty nested container should be considered equivalent to the absence of a key. The value type must have a copy method that copies all mutable state.

Methods Summary

copy()	Return a copy of the mapping.
get()	D.get(k[,d]) -> D[k] if k in D, else d.

Methods Documentation

copy() → NonemptyMapping[_K, _V]

Return a copy of the mapping.

This deep-copies values while referencing the default_factory callback and keys.

get(key: _K) → _V | None

get(key: _K, default: _T) → _V | _T

D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None.