Can Python Dictionaries Be Used Like Objects?

Can Python Dictionaries Emulate Object Attributes?

Accessing dictionary keys as object attributes offers convenience, but raises questions about potential issues. This article explores the usage of AttrDict, a custom class designed to address this need.

Custom Class Approach

To emulate object attributes for a dictionary, one can create a subclass called AttrDict:

class AttrDict(dict):
    def __getattr__(self, attr):
        return self[attr]
    def __setattr__(self, attr, value):
        self[attr] = value

Advantages of the Custom Class

• Convenience: Accessing keys as attributes with obj.foo syntax
• Automatic Synchronization: Attributes and items remain in sync
• Attribute Error Handling: Non-existent keys raise AttributeError instead of KeyError
• Tab Completion Support: Autocompletion for attributes

Disadvantages of the Custom Class

• Namespace Collision: Dictionary methods may be overwritten by key assignments
• Memory Leak: Issue in Python versions prior to 2.7.4/3.2.3
• Pylint Warnings: Triggers warnings for unexpected keyword arguments and missing member validation
• Complexity: May appear confusing to users unfamiliar with the underlying implementation

How it Works

The AttrDict class assigns itself as the internal __dict__ attribute of the object. This links the dictionary namespace to the object's attributes, allowing access via both syntaxes.

Python's Rationale for Not Providing This Feature

Python avoids the direct attribute access feature to prevent namespace pollution. Assigning dictionary items can potentially override method attributes, leading to unexpected behavior. For example:

d = AttrDict()
d.update({'items': ['jacket', 'necktie', 'trousers']})
for k, v in d.items():  # TypeError: 'list' object is not callable

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