khwilson commented on code in PR #43849:
URL: https://github.com/apache/arrow/pull/43849#discussion_r1733735774
##########
python/pyarrow/types.pxi:
##########
@@ -1618,59 +1618,79 @@ cdef class ExtensionType(BaseExtensionType):
Examples
--------
- Define a UuidType extension type subclassing ExtensionType:
+ Define a RationalType extension type subclassing ExtensionType:
>>> import pyarrow as pa
- >>> class UuidType(pa.ExtensionType):
- ... def __init__(self):
- ... pa.ExtensionType.__init__(self, pa.binary(16), "my_package.uuid")
- ... def __arrow_ext_serialize__(self):
- ... # since we don't have a parameterized type, we don't need extra
- ... # metadata to be deserialized
- ... return b''
- ... @classmethod
- ... def __arrow_ext_deserialize__(self, storage_type, serialized):
- ... # return an instance of this subclass given the serialized
- ... # metadata.
- ... return UuidType()
- ...
+ >>> import pyarrow.types as pt
+ >>> class RationalType(pa.ExtensionType):
+ ... def __init__(self, data_type: pa.DataType):
+ ... if not pt.is_integer(data_type):
+ ... raise TypeError(f"data_type must be an integer type not
{data_type}")
+ ... super().__init__(
+ ... pa.struct(
+ ... [
+ ... ("numer", data_type),
+ ... ("denom", data_type),
+ ... ],
+ ... ),
+ ... # N.B. This name does _not_ reference `data_type` so
deserialization
+ ... # will work for _any_ integer `data_type` after
registration
+ ... "my_package.rational",
+ ... )
+ ... def __arrow_ext_serialize__(self) -> bytes:
+ ... # No serialized metadata necessary
+ ... return b""
+ ... @classmethod
+ ... def __arrow_ext_deserialize__(self, storage_type, serialized):
+ ... # return an instance of this subclass given the serialized
+ ... # metadata
+ ... return RationalType(storage_type[0].type)
Register the extension type:
- >>> pa.register_extension_type(UuidType())
+ >>> pa.register_extension_type(RationalType(pa.int64()))
- Create an instance of UuidType extension type:
+ Create an instance of RationalType extension type:
- >>> uuid_type = UuidType()
+ >>> rational_type = RationalType(pa.int32())
Inspect the extension type:
- >>> uuid_type.extension_name
- 'my_package.uuid'
- >>> uuid_type.storage_type
- FixedSizeBinaryType(fixed_size_binary[16])
+ >>> rational_type.extension_name
+ 'my_package.rational'
+ >>> rational_type.storage_type
+ StructType(struct<numer: int32, denom: int32>)
Wrap an array as an extension array:
- >>> import uuid
- >>> storage_array = pa.array([uuid.uuid4().bytes for _ in range(4)],
pa.binary(16))
- >>> uuid_type.wrap_array(storage_array)
+ >>> storage_array = pa.array(
+ ... [
+ ... {"numer": 10, "denom": 17},
+ ... {"numer": 20, "denom": 13},
+ ... ],
+ ... type=rational_type.storage_type
+ ... )
+ >>> ratoinal_type.wrap_array(storage_array)
<pyarrow.lib.ExtensionArray object at ...>
- [
+ -- is_valid: all not null
...
- ]
Or do the same with creating an ExtensionArray:
- >>> pa.ExtensionArray.from_storage(uuid_type, storage_array)
+ >>> pa.ExtensionArray.from_storage(rational_type, storage_array)
Review Comment:
Done
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