provide deprecated key access mechanism

[mwfarb]

@hi-liang

class DeprecatedDict(dict):
    def __init__(self, *args, **kwargs):
        # Initialize with a standard dict, plus a set to track deprecated keys
        super().__init__(*args, **kwargs)
        self._deprecated_keys = set()
    def mark_deprecated(self, key):
        """Mark a key as deprecated."""
        if key in self:
            self._deprecated_keys.add(key)
        else:
            print(f"Warning: Key '{key}' does not exist in the dictionary.")
    def __getitem__(self, key):
        # If the key is deprecated, print a warning
        if key in self._deprecated_keys:
            print(f"Warning: Accessing deprecated key '{key}'.")
        # Return the actual value
        return super().__getitem__(key)
    def __delitem__(self, key):
        # Remove key from deprecated set if it's deleted
        self._deprecated_keys.discard(key)
        super().__delitem__(key)
    def is_deprecated(self, key):
        """Check if a key is marked as deprecated."""
        return key in self._deprecated_keys


# Initialize and add some items
my_dict = DeprecatedDict(a=1, b=2, c=3)
# Mark key 'b' as deprecated
my_dict.mark_deprecated('b')
# Accessing the key 'b' will trigger a warning
print(my_dict['b'])  # Output: Warning: Accessing deprecated key 'b'. \n 2
# Accessing non-deprecated key 'a' works normally
print(my_dict['a'])  # Output: 1
# Deleting 'b' will also remove it from the deprecated set
del my_dict['b']