ruamel.yaml ComposerError when using alias/ as name - ruamel.yaml

Question

I am trying to parse the following document
hello:
there: &there_value 1
foo:
*there_value: 3
This gets correctly parsed with the safe loader:
>>> from ruamel.yaml import YAML
>>> document = """
... hello:
... there: &there_value 1
... foo:
... *there_value: 3
"""
>>> yaml=YAML(typ="safe")
>>> yaml.load(document)
{'hello': {'there': 1}, 'foo': {1: 3}}
The round-trip (standard) loader throws an error:
>>> yaml=YAML()
>>> yaml.load(document)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "...\site-packages\ruamel\yaml\main.py", line 434, in load
return constructor.get_single_data()
File "...\site-packages\ruamel\yaml\constructor.py", line 119, in get_single_data
node = self.composer.get_single_node()
File "...\site-packages\ruamel\yaml\composer.py", line 76, in get_single_node
document = self.compose_document()
File "...\site-packages\ruamel\yaml\composer.py", line 99, in compose_document
node = self.compose_node(None, None)
File "...\site-packages\ruamel\yaml\composer.py", line 143, in compose_node
node = self.compose_mapping_node(anchor)
File "...\site-packages\ruamel\yaml\composer.py", line 223, in compose_mapping_node
item_value = self.compose_node(node, item_key)
File "...\site-packages\ruamel\yaml\composer.py", line 117, in compose_node
raise ComposerError(
ruamel.yaml.composer.ComposerError: found undefined alias 'there_value:'
in "<unicode string>", line 6, column 3:
*there_value: 3
^ (line: 6)
I am using Python 3.8.10, ruamel.yaml version 0.17.21.

Answer 1

As Anthon suggested in their comment, : is a valid character for an anchor,
so *there_value: is looking for there_value: which is not defined, only there_value is.
The solution is to add a space after the anchor, *there_value :.
hello:
there: &there_value 1
foo:
*there_value : 3
This loads correctly both with round-trip and with safe.