classes

21_Day_Classes_and_objects/21_classes_and_objects.md

@@ -9,10 +9,9 @@
 
 <sub>Author:
 <a href="https://www.linkedin.com/in/asabeneh/" target="_blank">Asabeneh Yetayeh</a><br>
-<small> First Edition: Nov 22 - Dec 22, 2019</small>
+<small>Second Edition: July, 2021</small>
 </sub>
 
-</div>
 </div>
 
 [<< Day 20](../20_Day_Python_package_manager/20_python_package_manager.md) | [Day 22 >>](../22_Day_Web_scraping/22_web_scraping.md)
@@ -30,22 +29,22 @@
     - [Inheritance](#inheritance)
     - [Overriding parent method](#overriding-parent-method)
   - [💻 Exercises: Day 21](#-exercises-day-21)
+    - [Exercises: Level 1](#exercises-level-1)
+    - [Exercises: Level 2](#exercises-level-2)
+    - [Exercises: Level 3](#exercises-level-3)
 
 # 📘 Day 21
 
 ## Classes and Objects
 
-Python is an object oriented programming language. Everything in Python is an object, with its properties and methods. A number, string, list, dictionary, tuple, set etc. used in a program is an object of a corresponding built-in class. We create class to create an object. A Class is like an object constructor, or a "blueprint" for creating objects. We instantiate a class to create an object. The class defines attributes and the behavior of the object, while the object, on the other hand, represents the class.
+Python is an object oriented programming language. Everything in Python is an object, with its properties and methods. A number, string, list, dictionary, tuple, set etc. used in a program is an object of a corresponding built-in class. We create class to create an object. A class is like an object constructor, or a "blueprint" for creating objects. We instantiate a class to create an object. The class defines attributes and the behavior of the object, while the object, on the other hand, represents the class.
 
 We have been working with classes and objects right from the beginning of this challenge unknowingly. Every element in a Python program is an object of a class.
-Let's check if everything in python is a class:
+Let us check if everything in python is a class:
 
 ```py
-Last login: Tue Dec 10 09:35:28 on console
-asabeneh@Asabeneh:~$ pyhton
--bash: pyhton: command not found
 asabeneh@Asabeneh:~$ python
-Python 3.7.5 (default, Nov  1 2019, 02:16:32)
+Python 3.9.6 (default, Jun 28 2021, 15:26:21)
 [Clang 11.0.0 (clang-1100.0.33.8)] on darwin
 Type "help", "copyright", "credits" or "license" for more information.
 >>> num = 10
@@ -86,6 +85,7 @@ class ClassName:
 ```py
 class Person:
   pass
+print(Person)
 ```
 
 ```sh
@@ -103,12 +103,13 @@ print(p)
 
 ### Class Constructor
 
-In the examples above, we have created an object from the Person class. However, Class without a constructor is not really useful in real applications. Let's use constructor function to make our class more useful. Like the constructor function in Java or JavaScript, python has also a built-in _**init**()_ constructor function. The _**init**_ constructor function has self parameter which is a reference to the current instance of the class
+In the examples above, we have created an object from the Person class. However, a class without a constructor is not really useful in real applications. Let us use constructor function to make our class more useful. Like the constructor function in Java or JavaScript, Python has also a built-in **__init__**() constructor function. The **__init__** constructor function has self parameter which is a reference to the current instance of the class
 **Examples:**
 
 ```py
 class Person:
       def __init__ (self, name):
+        # self allows to attach parameter to the class
           self.name =name
 
 p = Person('Asabeneh')
@@ -122,7 +123,7 @@ Asabeneh
 <__main__.Person object at 0x2abf46907e80>
 ```
 
-Let's add more parameters to the constructor function.
+Let us add more parameters to the constructor function.
 
 ```py
 class Person:
@@ -165,11 +166,9 @@ class Person:
           self.age = age
           self.country = country
           self.city = city
-
       def person_info(self):
         return f'{self.firstname} {self.lastname} is {self.age} years old. He lives in {self.city}, {self.country}'
 
-
 p = Person('Asabeneh', 'Yetayeh', 250, 'Finland', 'Helsinki')
 print(p.person_info())
 ```
@@ -181,7 +180,7 @@ Asabeneh Yetayeh is 250 years old. He lives in Helsinki, Finland
 
 ### Object Default Methods
 
-Sometimes, you may want to have a default values for you object methods. If we give default values for the parameters in the constructor, we can avoid errors when we call or instantiate our class without parameters. Let's see how it looks:
+Sometimes, you may want to have a default values for your object methods. If we give default values for the parameters in the constructor, we can avoid errors when we call or instantiate our class without parameters. Let's see how it looks:
 
 **Example:**
 
@@ -211,7 +210,7 @@ John Doe is 30 years old. He lives in Noman city, Nomanland.
 
 ### Method to Modify Class Default Values
 
-In the example below, the person class, all the constructor parameters have default values. In addition to that, we have skills parameter, which we can access using a method. Let's create add_skill method to add skills to the skills list.
+In the example below, the person class, all the constructor parameters have default values. In addition to that, we have skills parameter, which we can access using a method. Let us create add_skill method to add skills to the skills list.
 
 ```py
 class Person:
@@ -249,8 +248,8 @@ John Doe is 30 years old. He lives in Noman city, Nomanland.
 
 ### Inheritance
 
-Using inheritance we can reuse parent class code. Inheritance allows us to define a class that inherits all the methods and properties from another class. The parent class or super or base class is the class which gives all the methods and properties. Child class is the class that inherits from another class.
-Let's create a student class by inheriting from person class.
+Using inheritance we can reuse parent class code. Inheritance allows us to define a class that inherits all the methods and properties from parent class. The parent class or super or base class is the class which gives all the methods and properties. Child class is the class that inherits from another or parent class.
+Let us create a student class by inheriting from person class.
 
 ```py
 class Student(Person):
@@ -281,8 +280,8 @@ Lidiya Teklemariam is 28 years old. He lives in Espoo, Finland.
 ['Organizing', 'Marketing', 'Digital Marketing']
 ```
 
-We didn't call the _**init**()_ constructor in the child class. If we didn't call it then we can still access all the properties from the parent. But if we do call the constructor we can access the parent properties by calling _super_.  
-We can add a new method to the child or we can overwrite the parent class by creating the same method name in the child class. When we add the **init**() function, the child class will no longer inherit the parent's **init**() function.
+We did not call the **__init__**() constructor in the child class. If we didn't call it then we can still access all the properties from the parent. But if we do call the constructor we can access the parent properties by calling _super_.  
+We can add a new method to the child or we can override the parent class methods by creating the same method name in the child class. When we add the **__init__**() function, the child class will no longer inherit the parent's **__init__**() function.
 
 ### Overriding parent method
 
@@ -317,13 +316,15 @@ Lidiya Teklemariam is 28 years old. She lives in Espoo, Finland.
 ['Organizing', 'Marketing', 'Digital Marketing']
 ```
 
-We can use super() function or the parent name Person to automatically inherit the methods and properties from its parent. In the example above we override the parant method. The child method has a different feature, it can identify, if the gender is male or female and assign the proper pronoun(He/She).
+We can use super() built-in function or the parent name Person to automatically inherit the methods and properties from its parent. In the example above we override the parent method. The child method has a different feature, it can identify, if the gender is male or female and assign the proper pronoun(He/She).
 
-🌕 Now, you are fully charged with a super power of programming.  Now do some exercises for your brain and for your muscle.
+🌕 Now, you are fully charged with a super power of programming.  Now do some exercises for your brain and muscles.
 
 ## 💻 Exercises: Day 21
 
-1. Python has the module called _statistics_ and we can use this module to do all the statistical caluculations. However to challlenge ourselves, let's try to develop a program, which calculates the measure of central tendency of a sample (mean, median, mode) and measure of variability (range, variance, standard deviation). In addition to those measures, find the min, max, count, percentile, and frequency distribution of the sample. You can create a class called Statistics and create all the functions that do statistical calculations as methods for the Statistics class. Check the output below.
+### Exercises: Level 1
+
+1. Python has the module called _statistics_ and we can use this module to do all the statistical calculations. However, to learn how to make function and reuse function let us try to develop a program, which calculates the measure of central tendency of a sample (mean, median, mode) and measure of variability (range, variance, standard deviation). In addition to those measures, find the min, max, count, percentile, and frequency distribution of the sample. You can create a class called Statistics and create all the functions that do statistical calculations as methods for the Statistics class. Check the output below.
 
 ```py
 ages = [31, 26, 34, 37, 27, 26, 32, 32, 26, 27, 27, 24, 32, 33, 27, 25, 26, 38, 37, 31, 34, 24, 33, 29, 26]
@@ -357,7 +358,12 @@ Standard Deviation:  4.2
 Frequency Distribution: [(20.0, 26), (16.0, 27), (12.0, 32), (8.0, 37), (8.0, 34), (8.0, 33), (8.0, 31), (8.0, 24), (4.0, 38), (4.0, 29), (4.0, 25)]
 ```
 
-2. Create a class called PersonAccount. It has firstname, lastname, incomes, expenses properties and it has total_income, total_expense, account_info, add_income, add_expense and account_balance methods. Incomes is a set of incomes and its description. The same goes for expenses.
+### Exercises: Level 2
+
+1. Create a class called PersonAccount. It has firstname, lastname, incomes, expenses properties and it has total_income, total_expense, account_info, add_income, add_expense and account_balance methods. Incomes is a set of incomes and its description. The same goes for expenses.
+
+### Exercises: Level 3
+
 
 🎉 CONGRATULATIONS ! 🎉