Fokko commented on code in PR #4685:
URL: https://github.com/apache/iceberg/pull/4685#discussion_r868342529
##########
python/src/iceberg/schema.py:
##########
@@ -262,10 +267,45 @@ def primitive(self, primitive: PrimitiveType) -> T:
... # pragma: no cover
+@dataclass(init=True, eq=True)
+class Accessor:
+ """An accessor for a specific position in a container that implements the
StructProtocol"""
+
+ position: int
+ inner: Optional["Accessor"] = None
+
+ def __str__(self):
+ return f"Accessor(position={self.position},inner={self.inner})"
+
+ def __repr__(self):
+ return self.__str__()
+
+ def with_inner(self, accessor: "Accessor") -> "Accessor":
+ parent = copy.deepcopy(self)
+ acc = parent
+ while acc.inner:
+ acc = acc.inner
+ acc.inner = accessor
+ return parent
+
+ def get(self, container: StructProtocol) -> Any:
+ """Returns the value at self.position in `container`
+
+ Args:
+ container(StructProtocol): A container to access at position
`self.position`
+
+ Returns:
+ Any: The value at position `self.position` in the container
+ """
+ return container.get(self.position)
+
+
@singledispatch
def visit(obj, visitor: SchemaVisitor[T]) -> T:
"""A generic function for applying a schema visitor to any point within a
schema
+ The function traverses the schema in pre-order fashion
Review Comment:
For building the Accessors, the pre-order is much easier since we can just
wrap the field in the `inner` function. Also, I think it is much easier for
most people to reason because it follows the pattern of a recursive function.
I was looking at the existing `_IndexByName` visitor, and it looks like
we're actually using pre-order traversal as well. But mimicking this using the
before and after hooks:
https://github.com/apache/iceberg/blob/1bb526264b22372bf94a0d28ccf626da93ea6014/python/src/iceberg/schema.py#L391-L410
I could implement a similar pattern for creating the accessors. WDYT
@samredai ?
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