Magic Object Methods module completed

Author: ptyadana

12.Python Object Oriented Programming - JM/03.Magic Object Methods/magicattr.py

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+# Python Object Oriented Programming by Joe Marini course example
+# Using the __str__ and __repr__ magic methods
+
+
+class Book:
+    def __init__(self, title, author, price):
+        super().__init__()
+        self.title = title
+        self.author = author
+        self.price = price
+        self._discount = 0.1
+
+    # The __str__ function is used to return a user-friendly string
+    # representation of the object
+    def __str__(self):
+        return f"{self.title} by {self.author}, costs {self.price}"
+
+
+    # __getattribute__ called when an attr is retrieved. Don't
+    # directly access the attr name otherwise a recursive loop is created
+    # def __getattribute__(self, name):
+    #     if name == "price":
+    #         p = super().__getattribute__("price")
+    #         d = super().__getattribute__("_discount")
+    #         return p - (p*d)
+    #     return super().__getattribute__(name)
+
+
+    # __setattr__ called when an attribute value is set. Don't set the attr
+    # directly here otherwise a recursive loop causes a crash
+    def __setattr__(self, name, value):
+        if name == "price":
+            if type(value) is not float:
+                raise ValueError("price attribute needs to be float.")
+        return super().__setattr__(name, value)
+
+
+    # __getattr__ called when __getattribute__ lookup fails 
+    # you can pretty much generate attributes on the fly with this method
+    def __getattr__(self, name):
+        return name + " is not here"
+
+b1 = Book("War and Peace", "Leo Tolstoy", 39.95)
+b2 = Book("The Catcher in the Rye", "JD Salinger", 29.95)
+
+# b1.price =35
+# print(b1)
+
+# b2.price = 40
+# b2.price = float(40)
+# print(b2)
+
+print(b1.blahblah)

12.Python Object Oriented Programming - JM/03.Magic Object Methods/magiccall.py

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+# Python Object Oriented Programming by Joe Marini course example
+# Using the __str__ and __repr__ magic methods
+
+
+class Book:
+    def __init__(self, title, author, price):
+        super().__init__()
+        self.title = title
+        self.author = author
+        self.price = price
+
+    def __str__(self):
+        return f"{self.title} by {self.author}, costs {self.price}"
+
+    # the __call__ method can be used to call the object like a function
+    def __call__(self, title, author, price):
+        self.title = title
+        self.author = author
+        self.price = price
+
+
+
+b1 = Book("War and Peace", "Leo Tolstoy", 39.95)
+b2 = Book("The Catcher in the Rye", "JD Salinger", 29.95)
+
+# call the object as if it were a function
+print(b1)
+b1("Harry Potter", "JK.Rowling", 50.60)
+print(b1)

12.Python Object Oriented Programming - JM/03.Magic Object Methods/magiceq.py

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+# Python Object Oriented Programming by Joe Marini course example
+# Using the __str__ and __repr__ magic methods
+
+
+class Book:
+    def __init__(self, title, author, price):
+        super().__init__()
+        self.title = title
+        self.author = author
+        self.price = price
+
+    # the __eq__ method checks for equality between two objects
+    def __eq__(self, value):
+        if not isinstance(value, Book):
+            raise ValueError("can't compare Book to non-Book.")
+        return (self.title == value.title and
+        self.author == value.author and
+        self.price == value.price)
+
+    # the __ge__ establishes >= relationship with another obj
+    def __ge__(self, value):
+        if not isinstance(value, Book):
+            raise ValueError("can't compare Book to non-Book.")
+        return self.price >= value.price
+
+    # the __lt__ establishes < relationship with another obj
+    def __lt__(self, value):
+        if not isinstance(value, Book):
+            raise ValueError("can't compare Book to non-Book.")
+        return self.price < value.price
+        
+
+b1 = Book("War and Peace", "Leo Tolstoy", 39.95)
+b2 = Book("The Catcher in the Rye", "JD Salinger", 29.95)
+b3 = Book("War and Peace", "Leo Tolstoy", 39.95)
+b4 = Book("To Kill a Mockingbird", "Harper Lee", 24.95)
+
+# Check for equality
+print(b1 == b3)
+print(b1 == b2)
+# print(b1 == 42)
+
+# Check for greater and lesser value
+print(b1 >= b2)
+print(b1 < b2)
+
+# Now we can sort them too
+# python now will sort them by price ascending order
+books = [b1, b2, b3, b4]
+books.sort()
+print([book.title for book in books])

12.Python Object Oriented Programming - JM/03.Magic Object Methods/magicstr.py

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+# Python Object Oriented Programming by Joe Marini course example
+# Using the __str__ and __repr__ magic methods
+
+
+class Book:
+    def __init__(self, title, author, price):
+        super().__init__()
+        self.title = title
+        self.author = author
+        self.price = price
+
+    # use the __str__ method to return a string
+    def __str__(self):
+        return f"{self.title} by {self.author} costs {self.price}"
+
+    # use the __repr__ method to return an obj representation (for debugging purpose)
+    def __repr__(self):
+        return f"title: {self.title}, author: {self.author}, price: {self.price}"
+
+b1 = Book("War and Peace", "Leo Tolstoy", 39.95)
+b2 = Book("The Catcher in the Rye", "JD Salinger", 29.95)
+
+print(b1)
+print(b2)
+
+print(str(b2))
+print(repr(b2))