[Bug]: Invalid Timestamp and Complex Scalars Raise AttributeError and Crash

[tylzh97]

Summary

Timestamp and !!python/complex constructors lack guard clauses; invalid inputs lead to NoneType attribute access or ValueError from complex().

poc:

import yaml
yaml.safe_load("!!timestamp 'invalid'")
yaml.load("!!python/complex 'invalid'", Loader=yaml.FullLoader)

Traceback:

$ uv run python 
Python 3.10.18 (main, Sep  2 2025, 14:19:37) [Clang 20.1.4 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import yaml
>>> yaml.safe_load("!!timestamp 'invalid'")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/User/.venv/lib/python3.10/site-packages/yaml/__init__.py", line 125, in safe_load
    return load(stream, SafeLoader)
  File "/home/User/.venv/lib/python3.10/site-packages/yaml/__init__.py", line 81, in load
    return loader.get_single_data()
  File "/home/User/.venv/lib/python3.10/site-packages/yaml/constructor.py", line 51, in get_single_data
    return self.construct_document(node)
  File "/home/User/.venv/lib/python3.10/site-packages/yaml/constructor.py", line 55, in construct_document
    data = self.construct_object(node)
  File "/home/User/.venv/lib/python3.10/site-packages/yaml/constructor.py", line 100, in construct_object
    data = constructor(self, node)
  File "/home/User/.venv/lib/python3.10/site-packages/yaml/constructor.py", line 325, in construct_yaml_timestamp
    values = match.groupdict()
AttributeError: 'NoneType' object has no attribute 'groupdict'

Suggested Fix

• Confirm regex matches before dereferencing groups in construct_yaml_timestamp.
• Wrap complex() calls in try/except and surface ConstructorError.