Work with themes¶

These examples continue from the Item and theme created in the tutorial.

Update or clear themes¶

extension = ThemesExtension.ext(item)
themes = extension.themes
assert themes is not None
themes[0].concepts[0].title = "Climate science"
extension.themes = themes
assert item.properties["themes"][0]["concepts"][0]["title"] == "Climate science"

extension.themes = None
assert "themes" not in item.properties

Reading themes creates detached values. Assign them back after editing. Setting None removes the field but retains the extension declaration.

Catalogs, Collections, and summaries¶

catalog = pystac.Catalog(id="catalog", description="Thematic resources")
ThemesExtension.ext(catalog, add_if_missing=True).apply([theme])
assert catalog.extra_fields["themes"] == [theme.to_dict()]

collection = pystac.Collection(
    id="collection",
    description="Climate resources",
    extent=pystac.Extent(
        pystac.SpatialExtent([[-180, -90, 180, 90]]),
        pystac.TemporalExtent([[item.datetime, None]]),
    ),
    license="proprietary",
)
ThemesExtension.ext(collection, add_if_missing=True).apply([theme])
summaries = ThemesExtension.summaries(collection)
summaries.themes = [theme]
assert collection.extra_fields["themes"] == [theme.to_dict()]
assert collection.summaries.to_dict()["themes"] == [theme.to_dict()]

summaries.themes = None
assert "themes" not in collection.summaries.to_dict()

A Collection's own themes and its summaries are independent. The package does not aggregate themes from child Items automatically.

Manage extension membership¶

ThemesExtension.add_to(item)
assert ThemesExtension.has_extension(item)
ThemesExtension.ext(item).themes = None
ThemesExtension.remove_from(item)
assert not ThemesExtension.has_extension(item)

Clear theme metadata explicitly before removing the declaration when you want both removed.

Validate an Item¶

Install PySTAC's validation dependencies:

python -m pip install "pystac[validation]>=1,<2"

Populate themes before validating:

ThemesExtension.ext(item, add_if_missing=True).apply([theme])
item.validate()

Validation may fetch schemas over the network. apply(), property assignment, and serialization do not invoke validation. See validation boundaries.