Content for Udacity's Data Science Nanodegree curriculum (Term 2), which includes project and lesson content. Using Object-Oriented Programming, we will build a Python package for analyzing probability distributions.
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Object-oriented programming syntax
- procedural vs object-oriented programming
- classes, objects, methods and attributes
- coding a class
- magic methods
- inheritance
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Using object-oriented programming to make a Python package
- making a package
- tour of scikit-learn source code
- putting your package on PyPi
Another way to think about characteristics and actions is in terms of English grammar. A characteristic would be a noun. On the other hand, an action would be a verb.
Let's pick something from the real-world: a dog. A few characteristics could be the dog's weight, color, breed, and height. These are all nouns. What actions would a dog take? A dog can bark, run, bite and eat. These are all verbs.
- class - a blueprint consisting of methods and attributes
- object - an instance of a class. It can help to think of objects as something in the real world like a yellow pencil, a small dog, a blue shirt, etc. However, as you'll see later in the lesson, objects can be more abstract.
- attribute - a descriptor or characteristic. Examples would be color, length, size, etc. These attributes can take on specific values like blue, 3 inches, large, etc.
- method - an action that a class or object could take
- OOP - a commonly used abbreviation for object-oriented programming
- encapsulation - one of the fundamental ideas behind object-oriented programming is called encapsulation: you can combine functions and data all into a single entity. In object-oriented programming, this single entity is called a class. Encapsulation allows you to hide implementation details much like how the scikit-learn package hides the implementation of machine learning algorithms.
A function and a method look very similar. They both use the def keyword. They also have inputs and return outputs. The difference is that a method is inside of a class whereas a function is outside of a class.
If you instantiate two objects, how does Python differentiate between these two objects?
shirt_one = Shirt('red', 'S', 'short-sleeve', 15)
short_two = Shirt('yellow', 'M', 'long-sleeve', 20)
That's where self comes into play. If you call the change_price method on shirt_one, how does Python know to change the price of shirt_one and not of shirt_two?
shirt_one.change_price(12)
Behind the scenes, Python is calling the change_price method:
def change_price(self, new_price):
self.price = new_price
Self tells Python where to look in the computer's memory for the shirt_one object. And then Python changes the price of the shirt_one object. When you call the change_price```` method, shirt_one.change_price(12), self``` is implicitly passed in.
The word self is just a convention. You could actually use any other name as long as you are consistent; however, you should always use self rather than some other word or else you might confuse people. Other languages, like Javascript, might use the word this
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