Data Classes module completed

Author: ptyadana

12.Python Object Oriented Programming - JM/04.Data Classes/dataclass.py

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+# Python Object Oriented Programming by Joe Marini course example
+# Using data classes to represent data objects
+
+from dataclasses import dataclass
+#data classes are available for python 3.7 or later
+
+@dataclass
+class Book:
+    title : str
+    author : str
+    pages : int
+    price : float
+
+    def book_info(self):
+        return f"{self.title} by {self.author}"
+
+# create some instances
+b1 = Book("War and Peace", "Leo Tolstoy", 1225, 39.95)
+b2 = Book("The Catcher in the Rye", "JD Salinger", 234, 29.95)
+b3 = Book("War and Peace", "Leo Tolstoy", 1225, 39.95)
+
+# access fields
+print(b1.title)
+print(b2.author)
+
+# print the book itself - dataclasses implement __repr__
+# dataclass automatically creat __repr__
+print(b1)
+
+# comparing two dataclasses - they implement __eq__
+print(b1 == b3)
+print(b1 == b2)
+
+# TODO: change some fields
+b3.author = "JK.Rowling"
+b3.title = "Harry Potter"
+print(b3.book_info())

12.Python Object Oriented Programming - JM/04.Data Classes/datadefault.py

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+# Python Object Oriented Programming by Joe Marini course example
+# implementing default values in data classes
+
+from dataclasses import dataclass, field
+import random
+
+def price_func():
+    return float(random.randrange(20, 40))
+
+
+@dataclass
+class Book:
+    # you can define default values when attributes are declared
+    title: str = "No Title"
+    author: str = "No Author"
+    pages: int = 0
+    price: float = field(default_factory= price_func)
+
+
+
+b1 = Book("Harry Potter", "JK.Rowling", 14366)
+b2 = Book("Flip it", "M Heppel", 212)
+
+print(b1)
+print(b2)

12.Python Object Oriented Programming - JM/04.Data Classes/immutable.py

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+# Python Object Oriented Programming by Joe Marini course example
+# Creating immutable data classes
+
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)  # "The "frozen" parameter makes the class immutable
+class ImmutableClass:
+    value1: str = "Value 1"
+    value2: int = 0
+
+    def somefunc(self, newvalue):
+        self.value2 = newvalue
+
+obj = ImmutableClass()
+print(obj.value1)
+print(obj)
+
+# attempting to change the value of an immutable class throws an exception
+obj.value1 = "Some other value"
+print(obj.value1)
+
+# even functions within the class can't change anything
+obj.somefunc(50)
+print(obj)

12.Python Object Oriented Programming - JM/04.Data Classes/postinit.py

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+# Python Object Oriented Programming by Joe Marini course example
+# Using the postinit function in data classes
+
+from dataclasses import dataclass
+
+
+@dataclass
+class Book:
+    title: str
+    author: str
+    pages: int
+    price: float
+
+    # the __post_init__ function lets us customize additional properties
+    # after the object has been initialized via built-in __init__
+    def __post_init__(self):
+        self.description = f"{self.title} by {self.author}, {self.pages} pages"
+
+# create some Book objects
+b1 = Book("War and Peace", "Leo Tolstoy", 1225, 39.95)
+b2 = Book("The Catcher in the Rye", "JD Salinger", 234, 29.95)
+
+# use the description attribute
+print(b1.description)
+print(b2.description)