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.

Methods Summary

get()	D.get(k[,d]) -> D[k] if k in D, else d.
items()
keys()
values()

Methods Documentation

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.

items() → a set-like object providing a view on D's items

keys() → a set-like object providing a view on D's keys

values() → an object providing a view on D's values