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POHow to successfully "donate a book" as a function within a class
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  1. POHow to successfully "donate a book" as a function within a class
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    copied!<p>Let's say I have this virtual E-library and I have a function defined under a class that allows me to check if a book is in a given library BY ID NUMBER OF THE BOOK (which is an object) and if it isn't, I append it to the library. If I test it in a try-except block I keep getting the except message even though I know the ID number doesn't already exist. If someone can help me figure out this problem that would be good.</p> <pre><code> class Library: # the class constructor def __init__(self, books, patrons): self.books=books self.patrons=patrons def __str__(self): s="Patron(" for patron in self.patrons: s+=str(patron) + ', ' if len(self.patron) != 0: s= s[:-2] s+=']' for book in self.books: s+=str(book) + ', ' if len(self.books) != 0: s= s[:-2] s+='])' return s def __repr__(self): return str(self) def donate_book(self, book): for i in self.books: if i==book.book_id: raise DuplicateIdError() else: Library.append(book) </code></pre> <p>This is my try-except block:</p> <pre><code> try: donate_book(book) print("Thank you for your Donation!") except: print ("that id# is already taken, sorry") </code></pre> <p>my library was defined as an empty list library=[] is my try-except block code wrong or is my donate_book code wrong?</p> <p>my Book class:</p> <pre><code> class Book: # the class constructor def __init__(self, author, title, book_id): self.title = title self.author = author self.book_id = book_id def __str__(self): s = "Books("+self.author+", "+self.title+", "+self.book_id+")" return s def __repr__(self): return str(self) </code></pre> <p>I defined duplicate error as this:</p> <pre><code>class DuplicateIdError(Exception): #the class constructor def __init__(self, ident): self.ident= ident def __str__(self): s= print("'duplicate identificatoin: #" + self.ident + ".'") return s # returns a string rep matching def __repr__(self): return str(self) </code></pre>
 

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