If you’re looking for an implementation of an InfiniteDefaultRevisionDictionary, it sounds like you’re interested in a dictionary that automatically handles missing keys by creating default values for them, and possibly, keeps a revision history for each key. Python’s standard collections.defaultdict can be used as a basis for creating default values, but it doesn’t track revisions out of the box. We’ll need to extend its functionality.
I’ll guide you through creating a custom class that acts like a defaultdict, but also maintains a revision history for each key. This will involve subclassing Python’s built-in dict and integrating revision tracking.
Step 1: Define the Class
We’ll create a class called InfiniteDefaultRevisionDictionary that initializes with a factory function for creating default values and uses an internal dictionary to track revisions.
Step 2: Implement Default Value Creation and Revision Tracking
Every time a key is accessed or set, the class will ensure that there’s a default value (using the provided factory function) and track the access or change as a new revision.
Step 3: Provide Methods to Retrieve Revisions
We’ll add methods to retrieve the current revision number for a key and to get the value of a key at a specific revision.
Here’s a basic implementation:
class InfiniteDefaultRevisionDictionary(dict):
def __init__(self, default_factory=None, *args, **kwargs):
super().__init__(*args, **kwargs)
self.default_factory = default_factory
self.revisions = {}
def __missing__(self, key):
if self.default_factory is None:
raise KeyError(key)
value = self[key] = self.default_factory()
self.revisions[key] = [(0, value)]
return value
def __setitem__(self, key, value):
revision = self.revisions.get(key, [])
revision_number = revision[-1][0] + 1 if revision else 0
revision.append((revision_number, value))
self.revisions[key] = revision
super().__setitem__(key, value)
def get_revision(self, key, revision_number):
if key in self.revisions:
for rev, value in reversed(self.revisions[key]):
if rev <= revision_number:
return value
return None # or raise an exception, based on how strict you want to be
def current_revision(self, key):
if key in self.revisions:
return self.revisions[key][-1][0]
return None # Key does not exist
# Example usage
default_factory = list # Using list as a simple example of a default factory
d = InfiniteDefaultRevisionDictionary(default_factory)
# Accessing a missing key to trigger default value creation
print(d['missing_key']) # Should print an empty list: []
# Modifying the value and checking revisions
d['missing_key'].append('first_revision')
d['missing_key'] = ['second_revision']
print(d.get_revision('missing_key', 0)) # first_revision
print(d.get_revision('missing_key', 1)) # second_revision
This example is quite basic and can be extended with more features, such as better error handling, a method to retrieve the entire revision history of a key, or optimizations for memory usage when tracking revisions of large objects. Depending on your specific needs, you might also consider using weak references for the revision history to avoid preventing garbage collection of unreferenced objects.
Reference Links to Include:
Python Data Structures:
- Introduction and best practices for using advanced data structures in Python.
- Suggested Search: “Python data structures tutorial”
Custom Python Dictionaries:
- Detailed guides or tutorials on creating custom dictionary types, similar to InfiniteDefaultRevisionDictionary.
- Suggested Search: “Custom dictionary Python tutorial
Python Coding Examples:
- Practical examples and use cases for implementing custom functionalities in Python dictionaries.
Stack Overflow for Python Programming Questions:
- A platform for troubleshooting and advice on Python programming, especially related to custom data structures.
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