database - How to create Set from Pydblite in Python -

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hello i'm using pydblite in order store url in python database. script add urls time in database want delete duplicate (or make set) keeping 1 same url @ ending of program.

i have 2 fields url , date: 

    self.db = base('url_database.pdl')     self.db.create('url', 'date', mode="open")


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