PyYAML 5.4/5.4.1 breaks YAML loader

[jamesjer]

Current Behavior

The latest attempt to build networxk 2.5 for Fedora failed to pass the test suite:

=================================== FAILURES ===================================
___________________________ TestYaml.testUndirected ____________________________

self = <networkx.readwrite.tests.test_yaml.TestYaml object at 0x7f57aad7f550>

    def testUndirected(self):
>       self.assert_equal(self.G, data=False)

networkx/readwrite/tests/test_yaml.py:44: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
networkx/readwrite/tests/test_yaml.py:35: in assert_equal
    Gin = nx.read_yaml(fname)
<decorator-gen-682>:2: in read_yaml
    ???
networkx/utils/decorators.py:239: in _open_file
    result = func_to_be_decorated(*new_args, **kwargs)
networkx/readwrite/nx_yaml.py:91: in read_yaml
    G = yaml.load(path, Loader=yaml.FullLoader)
/usr/lib64/python3.10/site-packages/yaml/__init__.py:114: in load
    return loader.get_single_data()
/usr/lib64/python3.10/site-packages/yaml/constructor.py:51: in get_single_data
    return self.construct_document(node)
/usr/lib64/python3.10/site-packages/yaml/constructor.py:55: in construct_document
    data = self.construct_object(node)
/usr/lib64/python3.10/site-packages/yaml/constructor.py:100: in construct_object
    data = constructor(self, node)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <yaml.loader.FullLoader object at 0x7f57aad7fd00>
node = MappingNode(tag='tag:yaml.org,2002:python/object:networkx.classes.graph.Graph', value=[(ScalarNode(tag='tag:yaml.org,2...=[])), (ScalarNode(tag='tag:yaml.org,2002:str', value='g'), MappingNode(tag='tag:yaml.org,2002:map', value=[]))]))]))])

    def construct_undefined(self, node):
>       raise ConstructorError(None, None,
                "could not determine a constructor for the tag %r" % node.tag,
                node.start_mark)
E       yaml.constructor.ConstructorError: could not determine a constructor for the tag 'tag:yaml.org,2002:python/object:networkx.classes.graph.Graph'
E         in "/tmp/tmpkqn21u1g", line 1, column 1

/usr/lib64/python3.10/site-packages/yaml/constructor.py:427: ConstructorError

Identical failures happened for testDirected and testMultiGraph. This is due to the fix for CVE-2020-14343 that was included in the PyYAML 5.4 release. See yaml/pyyaml#420.

Expected Behavior

The test suite should pass.

Steps to Reproduce

Run the test suite with PyYAML 5.4 or 5.4.1 installed.

Environment

Python version: 3.10a4 (but the same issue occurs with 3.9)
NetworkX version: 2.5

Additional context

https://access.redhat.com/security/cve/cve-2020-14343

[MridulS]

Can you test the build with the latest master branch too? a6dd458 should have fixed it.

[jamesjer]

Indeed, building from master works. Thank you for the quick response. I will patch the Fedora package with a6dd458 for now until the next NetworkX release.