How Do I Efficiently Remove Duplicate Objects from a Python List While Preserving Order?

Efficiently Handling Duplicate Objects with Python

In Python, it can be necessary to remove duplicate objects from a list while maintaining the original order. This issue arises when you have a list of custom objects and want to filter duplicates based on certain criteria or check for duplicates in a database.

Regarding your specific requirements, you need to define uniqueness within your objects to effectively use the set(list_of_objects) method. This involves making your objects hashable by implementing the eq and hash methods.

The eq method defines object equality. For example, if you have Book objects with author_name and title attributes, where the combination of author and title is unique, the eq method might look like this:

<code class="python">def __eq__(self, other):
    return self.author_name == other.author_name and self.title == other.title</code>

Similarly, the hash method generates a hash value for the object. A common approach is to hash a tuple of key attributes:

<code class="python">def __hash__(self):
    return hash(('title', self.title, 'author_name', self.author_name))</code>

With these methods in place, you can now remove duplicates from a list of Book objects:

<code class="python">books = [Book('title1', 'author1'), Book('title2', 'author2'), Book('title1', 'author1')]
unique_books = list(set(books))</code>

Furthermore, to check for duplicates in a database, you can use the following approach:

<code class="python">import sqlalchemy

session = sqlalchemy.orm.sessionmaker()()
records = session.query(YourModel).all()
existing_titles = set([record.title for record in records])
unique_objects = [obj for obj in objects if obj.title not in existing_titles]</code>

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