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Creating and using objects

From: Python 3 Essential Training

Video: Creating and using objects

Python is fundamentally an object-oriented language. In fact, in Python 3 everything is an object. So let's look at how we can create our own objects. We'll start by making a working copy of syntax.py. I'll call this syntax-objects.py. And we'll open our working copy. Now we'll go into a lot more detail on objects later on. The point here is just to get a handle on the syntax of creating objects.

Creating and using objects

Python is fundamentally an object-oriented language. In fact, in Python 3 everything is an object. So let's look at how we can create our own objects. We'll start by making a working copy of syntax.py. I'll call this syntax-objects.py. And we'll open our working copy. Now we'll go into a lot more detail on objects later on. The point here is just to get a handle on the syntax of creating objects.

So we'll go ahead and start by defining a class. Now a class is the definition that's used when creating an object in Python. So we'll use the class keyword, and we'll call this class Egg. And the first thing we'll define inside of the class is a constructor. And a constructor in Python is a method, or a function inside the class, and has a special name which is __init__, like that. And all methods within classes have self as the first argument.

This is a reference to the object itself. And it's traditionally called self. It's not required, but it's a really, really good idea to always call it self. And following self can be arguments that can be used in constructing the object. And in this case we are going to say how do you want your eggs? And so it'll be a kind of eggs, and we'll call it kind, and we'll give it a default value of fried. And then we will assign this value to an object variable.

And object variables are referenced to the object itself, so we'll say self.kind = kind, and that will create an object variable that will be carried around and encapsulated in the object. And so each instance of this class, each object, can have a different value for kind. Now let's define a method for finding out what kind. And we'll call this whatKind, and it has self as the only argument.

And we'll simply return self.kind. Now we have a class. It's a very simple class, and it doesn't do anything terribly useful, but it's good as an example of the syntax of how you create a class. And now we'll go ahead and create an object. Now an object is an instance of a class. You can think of the class as like the blueprint. This defines how the object is created, and the object itself is an instance. The object is an encapsulation of all of the methods and the variables that are inside of the class.

And so we'll say fried = Egg, like that. And that will create a object called fried, based on the class, Egg. And you notice we don't have anything in the parentheses, so it will use this default value when it creates or constructs the object. The constructor is called every time you create an object. So here we've created an object with the assignment operator. And so the first thing it'll do is it'll call this Constructor, and it'll assign this default value.

We can also create a scrambled egg, like this. And so when we print these out, later on we can say print(fried.whatKind()). And if we save this and run it, it says that it's a fried egg. Instead of the fried kind, I used the scrambled kind, and this is just this different object, but it's using exactly the same interface.

If I save it and run it, now we have a scrambled egg. So this is just a very simple and a very simplistic example of how an object is created. We have a definition, which is called a class, and this defines the blueprint of how these objects are made. And then we have a couple of objects that are created using that class. And so these are considered instances of that class, or objects. And these objects are completely functional, and they contain data, and they contain code in the form of these methods, and that is how you define and create objects in Python.

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This video is part of

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Python 3 Essential Training

87 video lessons · 39604 viewers

Bill Weinman
Author

 
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  1. 5m 14s
    1. Welcome
      1m 32s
    2. Understanding prerequisites for Python
      2m 4s
    3. Using the exercise files
      1m 38s
  2. 33m 29s
    1. Getting started with "Hello World"
      4m 43s
    2. Selecting code with conditionals
      4m 45s
    3. Repeating code with a loop
      4m 13s
    4. Reusing code with a function
      2m 43s
    5. Creating sequences with generator functions
      2m 46s
    6. Reusing code and data with a class
      4m 39s
    7. Greater reusability with inheritance and polymorphism
      7m 17s
    8. Handling errors with exceptions
      2m 23s
  3. 22m 32s
    1. Installing Python 3 and Eclipse for Windows
      11m 24s
    2. Installing Python 3 and Eclipse for Mac
      11m 8s
  4. 28m 0s
    1. Creating a main script
      3m 27s
    2. Understanding whitespace in Python
      4m 8s
    3. Commenting code
      3m 28s
    4. Assigning values
      3m 37s
    5. Selecting code and values with conditionals
      4m 46s
    6. Creating and using functions
      3m 54s
    7. Creating and using objects
      4m 40s
  5. 31m 23s
    1. Understanding variables and objects in Python
      2m 46s
    2. Distinguishing mutable and immutable objects
      2m 41s
    3. Using numbers
      3m 34s
    4. Using strings
      6m 38s
    5. Aggregating values with lists and tuples
      4m 55s
    6. Creating associative lists with dictionaries
      4m 24s
    7. Finding the type and identity of a variable
      4m 45s
    8. Specifying logical values with True and False
      1m 40s
  6. 9m 42s
    1. Selecting code with if and else conditional statements
      2m 22s
    2. Setting multiple choices with elif
      2m 14s
    3. Understanding other strategies for multiple choices
      2m 38s
    4. Using the conditional expression
      2m 28s
  7. 11m 26s
    1. Creating loops with while
      1m 27s
    2. Iterating with for
      3m 54s
    3. Enumerating iterators
      3m 22s
    4. Controlling loop flow with break, continue, and else
      2m 43s
  8. 23m 28s
    1. Performing simple arithmetic
      2m 14s
    2. Operating on bitwise values
      3m 30s
    3. Comparing values
      3m 32s
    4. Operating on Boolean values
      2m 59s
    5. Operating on parts of a container with the slice operator
      6m 52s
    6. Understanding operator precedence
      4m 21s
  9. 11m 34s
    1. Using the re module
      1m 4s
    2. Searching with regular expressions
      3m 12s
    3. Replacing with regular expressions
      3m 29s
    4. Reusing regular expressions with re.compile
      3m 49s
  10. 9m 10s
    1. Learning how exceptions work
      1m 18s
    2. Handling exceptions
      4m 15s
    3. Raising exceptions
      3m 37s
  11. 23m 1s
    1. Defining functions
      6m 23s
    2. Using lists of arguments
      2m 26s
    3. Using named function arguments
      4m 32s
    4. Returning values from functions
      1m 55s
    5. Creating a sequence with a generator function
      7m 45s
  12. 47m 29s
    1. Understanding classes and objects
      5m 12s
    2. Using methods
      6m 12s
    3. Using object data
      10m 4s
    4. Understanding inheritance
      5m 11s
    5. Applying polymorphism to classes
      7m 13s
    6. Using generators
      9m 48s
    7. Using decorators
      3m 49s
  13. 18m 54s
    1. Understanding strings as objects
      3m 25s
    2. Working with common string methods
      5m 24s
    3. Formatting strings with str.format
      5m 31s
    4. Splitting and joining strings
      2m 49s
    5. Finding and using standard string methods
      1m 45s
  14. 25m 27s
    1. Creating sequences with tuples and lists
      4m 6s
    2. Operating on sequences with built-in methods
      5m 50s
    3. Organizing data with dictionaries
      4m 56s
    4. Operating on character data with bytes and byte arrays
      10m 35s
  15. 11m 46s
    1. Opening files
      2m 4s
    2. Reading and writing text files
      4m 33s
    3. Reading and writing binary files
      5m 9s
  16. 21m 27s
    1. Creating a database with SQLite 3
      6m 56s
    2. Creating, retrieving, updating, and deleting records
      7m 31s
    3. Creating a database object
      7m 0s
  17. 18m 27s
    1. Using standard library modules
      8m 0s
    2. Finding third-party modules
      5m 47s
    3. Creating a module
      4m 40s
  18. 23m 11s
    1. Dealing with syntax errors
      8m 19s
    2. Dealing with runtime errors
      4m 0s
    3. Dealing with logical errors
      4m 22s
    4. Using unit tests
      6m 30s
  19. 19m 56s
    1. Normalizing a database interface
      6m 39s
    2. Deconstructing a database application
      8m 9s
    3. Displaying random entries from a database
      5m 8s
  20. 29s
    1. Goodbye
      29s

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