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When writing code in the Python programming language, you use comments to isolate portions of the program that you don’t want the interpreter to run.

• Document a program
• Isolate a portion of a program during debugging
• Make code more understandable to the programmer

## Creating a Comment

To create a comment in the Python programming language, the # symbol is used.

# can be used above a line of code or inline.

```#This is a comment
print("Hello, World!")

print("Hello, World!") #This is a comment
```

In the Python programming language, multiline comments don’t exists. However, you can use the docstring which are made using the “”””””.

```"""
This is a comment
written in
more than just one line
"""
print("Hello, World!")
```

The docstring is specifically meant for documenting a method or function in the Python programming langauge.

## Conclusion

Comments are used in programming languages to document, debug and make code understandable. They can be single line comments or multiline comments.

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## Arithmetic Operators

There are seven basic arithmetic operators in the Python programming language.

They are:

2. Subtraction
3. Multiplication
4. Division
5. Integer Division
6. Exponentiation
7. Modulus

This is represented by the + symbol. It adds two numbers together and gives their sum.

## Subtraction

This is represented by the – operator. It takes the value on the right from the value on the left to give the difference ot the two values.

## Multiplication

This is represented by the * operator. It multiplies the value on the left with the value on the right to give a product of the two.

## Division

This is represented by the / operator. It divides the value on the left with the value on the right to give the quotient.

## Integer Division

This is a special form of division represented by //. It gives the whole number value of the quotient.

## Exponentiation

This is represented by the ** operator. It gives the result of a value raised to another value.

## Modulus

This is the remainder of division of one number by another number. It is used to test if the number on the right is a factor of the number of the left.

## Conclusion

The above operators are how arithmetic is done in the Python programming language on a basic level.

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## Statements and Expressions

Computers as machines deal work with data. Data is processed by the computer under the control of a program.

The program takes the data as input, processes it and produces an output.

The code that powers the programs does so using statements and expressions.

## Statements

A statement is an instruction that tells the computer to do something. They carry out an action in the code for a computer program.

On Day 1, you used the assignment statement. The assignment statement is represented by “=”. When you created a variable, the assignment statement is used to set its value.

An assignment statement associates a value with a variable.

Another assignment statement we have seen so far is the print statement. The print statement displays a value placed within it by the user.

## Expressions

An expression is a piece of code that returns data. Expressions are a sequence of values, joined by operators that can be simplified to other values.

For example, 2 + 2 is an expression representing the value 4.

Expressions are evaluated by the Python interpreter. If you type in an expression into the Python interpreter, it evaluates it and displays the result.

The first line is an expression that has a value of 5. When 1 + 1 is added, we get 2 so that is also an expression.

x = 5 is the assignment statement in action. x = x + 1 will take the current value in x on the right-hand side and add 1 to it. Then assign that value back to x.

The print statement displays the value in the x variable which is 6.

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## Variables and Data Types

As I see it, the purpose of programming is to build machines out of bytes that are impossible or too expensive to build out of atoms. Computers are machines that can imitate any other machine. Programming is the act of making them do that.

Eric Hodges

From the above quote, we can see that a computer is a universal machine.

As we begin the journey of learning how to program on this site, the following characteristics of universal machines will shape the content for this training.

1. A way to keep track
2. A way to make decisions
3. A way to keep going

We achieve the first feature by using variables. The second feature is implemented using branching while the third feature is implemented using loops.

This post will focus on variables. Variables are a container for information, they are used to store values in a program.

The way variables are created in the Python programming language is similar to how they are treated in algebra.

if x = 6, what is x?

If you know algebra, you would answer 6 and you would be right. Like in algebra, the = symbol is for assignment. It assigns the value on the right to the value on the left.

A variable is created the moment you assign a value to it. Once we assign a value to a variable, the Python interpreter creates it.

In the last post about Input and Output, a variable name was created when the input from the user was assigned to it.

Like containers in the real world, the type of material a container is made out of determines what kind of material it can store. In computing, this is the concept of data types.

In the Python programming language, we have 5 standard data types:

1. Numbers
2. String
3. List
4. Tuple
5. Dictionary

For this program, we shall only look at numbers. However, I will illustrate Numbers and Strings in this blog post.

We have two types of numbers in computing: integers and decimals. Integers are whole numbers while decimals have a . in them for example, 1 is an integer while 1.0 is a decimal.

Strings are a sequence of characters. Your name is a sequence of characters. Strings are placed in the “”.

The type function will let you know the data type of the variable passed into it. The code below will illustrate the concept in action.

The above image shows that in the first 3 lines we declare the respective variables. Do bear in mind that the variable names are for you, not the users.

Once we use the type function, notice that it gives us the type each variable. The decimal variable is depicted as a float.

## Content and Context

This is a very important concept when choosing the data type of a variable. The “label” of a variable is different from its content.

As a result of this, you cannot declare the phone number of a user as either an integer or a float because you cannot add two phone numbers together.

Rather you would define them as a string. As seen in the blog post on Input and Output, you have to convert a number to a string before you can join it to it.

This is important as we continue on our journey.

## Learn Python in One Week

If you want a quick and easy introduction to the Python programming language, you should check out my fifth book: Learn Python in One Week on the Amazon store.

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## Input and Output

No program would be complete is it didn’t have a way to receive input from the user.

To receive input from the user in the Python programming language, we use the input() function.

The input() function is assigned to a value called a variable. Text is placed in between the brackets which serve as a prompt for the user.

The code above shows how to receive a value from the user. The value is then stored in a variable called name.

The value inside the name variable can then be printed out to the screen.

## Concatenation

Concatenation is the joining of strings. In the Python programming language, the “+” is the concatenation operator.

In the example above, when you have a number, you must convert it to a string before you can concatenate it.

```length = input("Please enter the length of the square: ")
length = int(length)
area = length * length
print("The area of a square of length", length, "is", area)
```

Above is a simple program to find the area of a square. On line 2, the value received by the user is converted into an integer.

On line 4 when we print the output, we get the following output:

Note that the output has added spaces whereas, in the original program, we had none.

Overloading simply means that there are many ways to call a function.

## Learn Python in One Week

If you want a quick and easy introduction to the Python programming language, you should check out my fifth book: Learn Python in One Week on the Amazon store.