Data Class Examples

returnvalue · returnvalue · commit ab65631afd29 · 2020-09-30T12:01:33.000-04:00
diff --git a/README.md b/README.md
@@ -38,4 +38,5 @@ files, and the full tutorial for each collection of code is available below. 
 31. [Multiple Inheritance In Python](https://vegibit.com/multiple-inheritance-in-python/)
 32. [Python Interface Design Pattern](https://vegibit.com/python-interface-design-pattern/)
 33. [Composition Over Inheritance](https://vegibit.com/composition-over-inheritance/)
-34. [What Are Python Magic Methods](https://vegibit.com/what-are-python-magic-methods/)
+34. [What Are Python Magic Methods](https://vegibit.com/what-are-python-magic-methods/)
+35. [Python Data Class](https://vegibit.com/python-data-class/)
diff --git a/dataclass.py b/dataclass.py
@@ -0,0 +1,159 @@
+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}'
+
+    def __repr__(self):
+        return f'title={self.title},author={self.author},price={self.price}'
+
+
+book1 = Book('Python Crash Course', 'Eric Matthes', 23.99)
+book2 = Book('Serious Python', 'Julien Danjou', 25.43)
+
+# print each object
+print(book1)
+print(book2)
+# Python Crash Course by Eric Matthes, costs 23.99
+# Serious Python by Julien Danjou, costs 25.43
+
+# use str() and repr()
+print(str(book1))
+print(repr(book2))
+# Python Crash Course by Eric Matthes, costs 23.99
+# title=Serious Python,author=Julien Danjou,price=25.43
+
+
+from dataclasses import dataclass
+
+
+@dataclass
+class Book():
+    title: str
+    author: str
+    price: float
+
+    def __str__(self):
+        return f'{self.title} by {self.author}, costs {self.price}'
+
+    def __repr__(self):
+        return f'title={self.title},author={self.author},price={self.price}'
+
+
+book1 = Book('Python Crash Course', 'Eric Matthes', 23.99)
+book2 = Book('Serious Python', 'Julien Danjou', 25.43)
+
+# print each object
+print(book1)
+print(book2)
+# Python Crash Course by Eric Matthes, costs 23.99
+# Serious Python by Julien Danjou, costs 25.43
+
+# use str() and repr()
+print(str(book1))
+print(repr(book2))
+# Python Crash Course by Eric Matthes, costs 23.99
+# title=Serious Python,author=Julien Danjou,price=25.43
+
+
+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
+book1 = Book('Python Crash Course', 'Eric Matthes', 544, 23.99)
+book2 = Book('Serious Python', 'Julien Danjou', 225, 25.43)
+
+# use the description attribute
+print(book1.description)
+print(book2.description)
+# Python Crash Course by Eric Matthes, 544 pages
+# Serious Python by Julien Danjou, 225 pages
+
+
+from dataclasses import dataclass, field
+
+
+@dataclass
+class Book:
+    # you can define default values when attributes are declared
+    title: str = 'Empty Book'
+    author: str = 'Your Imagination'
+    pages: int = 0
+    price: float = 0.0
+
+
+# Create a default book object
+book1 = Book()
+print(book1)
+
+# Create a specified book, price is set by field operator
+book1 = Book('Python Crash Course', 'Eric Matthes', 544, 23.99)
+book2 = Book('Serious Python', 'Julien Danjou', 225, 25.43)
+print(book1)
+print(book2)
+# Book(title='Empty Book', author='Your Imagination', pages=0, price=0.0)
+# Book(title='Python Crash Course', author='Eric Matthes', pages=544, price=23.99)
+# Book(title='Serious Python', author='Julien Danjou', pages=225, price=25.43)
+
+
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class Book:
+    title: str
+    author: str
+    pages: int
+    price: float
+
+    # You can define methods in a dataclass like any other
+    def bookinfo(self):
+        return f'{self.title}, by {self.author}'
+
+
+# create some instances
+book1 = Book('Python Crash Course', 'Eric Matthes', 544, 23.99)
+book2 = Book('Serious Python', 'Julien Danjou', 225, 25.43)
+
+# access fields
+print(book1.title)
+print(book2.author)
+
+# print the book itself - dataclasses provide a default
+# implementation of the __repr__ function
+print(book1)
+
+# comparing two dataclasses
+book3 = Book('Automate the Boring Stuff with Python', 'Al Sweigart ', 592, 26.99)
+print(book1 == book3)
+
+# change some fields, call a regular class method
+book1.title = 'Python for Kids'
+book1.pages = 864
+print(book1.bookinfo())
+# Python Crash Course
+# Julien Danjou
+# Book(title='Python Crash Course', author='Eric Matthes', pages=544, price=23.99)
+# False
+# Traceback (most recent call last):
+#   File "C:/python/OOP/dataclass.py", line 33, in
+#     book1.title = 'Python for Kids'
+#   File "", line 3, in __setattr__
+# dataclasses.FrozenInstanceError: cannot assign to field 'title'
