DOC: document late-binding behavior of Transformer serialization methods#1604
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madhavcodez wants to merge 1 commit into
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DOC: document late-binding behavior of Transformer serialization methods#1604madhavcodez wants to merge 1 commit into
madhavcodez wants to merge 1 commit into
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Transformer.from_crs builds a PROJ late-binding transformer that defers selecting a concrete transformation until transform() is called. Until then to_wkt() and to_json() return None and to_json_dict() raises TypeError, none of which the docstrings mentioned, so downstream code that trusted the documented str/dict return crashed. Add a Notes section to to_wkt, to_json, and to_json_dict describing the late-binding case and the two workarounds (get_last_used_operation after transform, or TransformerGroup), qualify the Returns of to_wkt/to_json to allow None, and add a history entry. Closes pyproj4#1549
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Summary
A
Transformerbuilt withTransformer.from_crs(...)is late-binding: PROJ does not select a concrete operation untiltransform()is called with coordinates. Until thento_json()andto_wkt()returnNone, andto_json_dict()raisesTypeError: the JSON object must be str, bytes or bytearray, not NoneType(#1549). The docstrings did not mention this, so theNoneand theTypeErrorlook like bugs.Changes
to_json,to_wkt, andto_json_dictdocstrings, including the two ways to obtain a serializable operation: callget_last_used_operation()aftertransform()(PROJ 9.1+), or build aTransformerGroupand serialize one of its candidate operations.to_json/to_wktreturnNonewhileto_json_dictraisesTypeError.Returnsofto_json/to_wktasstr or None.docs/history.rstentry.Docs only, no behavior change.
Closes #1549