rdblue commented on code in PR #4685:
URL: https://github.com/apache/iceberg/pull/4685#discussion_r868270096
##########
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:
I don't think this change is a good idea. We use the visitor to create or
process tree structures quite a bit and the post-order traversal works well in
most cases because the visitor is passed the result of visiting children. For
building accessors, the post-order traversal creates all of the child accessors
so each level adds a new wrapper and returns a map with an additional accessor
level.
Changing this pattern requires changing quite a bit of code and I think
makes the visitor you're building here more complicated because it can't rely
on traversal to create the child accessors it needs. I'd recommend not changing
the order.
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