Variables

Variables#

Variables store data in a computer’s memory. A variable refers to a memory address in which data is stored. A variable can have a short name (like x, y, z), but a more descriptive name (firstname, lastname, age, country) is highly recommended. Number at the beginning, special character, hyphen are not allowed when naming a variable.

Python Variable Naming Rules#

  • A variable name must start with a letter or the underscore character

  • A variable name cannot start with a number

  • A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )

  • Variable names are case-sensitive (firstname, Firstname, FirstName and FIRSTNAME) are different variables)

Here are some example of valid variable names:

  • first_name

  • last_name

  • firstname

  • lastname

  • age

  • country

  • city

  • capital_city

  • _if # when we want to use reserved word as a variable

  • year_2021

  • year2021

  • current_year_2021

  • birth_year

  • num1

  • num2

Invalid variables names:

  • first-name

  • first@name

  • first$name

  • num-1

  • 1num

We will use standard Python variable naming style which has been adopted by many Python developers, which is the snake case (snake_case) variable naming convention. We use an underscore character after each word for a variable containing more than one word (eg. first_name, engine_rotation_speed, day_of_week). The example below is an example of standard naming of variables, underscore is required when the variable name is more than one word.

When we assign a certain data type to a variable, it is called a variable declaration. For instance in the example below my first name is assigned to a variable first_name. The equal sign is an assignment operator. Assigning means storing data in the variable. The equal sign in Python is not equality as in Mathematics.

Example:

# Variables in Python
first_name = "Aurora"
last_name = "Luna"
country = "Indonesia"
city = "Palembang"
age = 6
is_student = True
skills = ["HTML", "CSS", "JS", "React", "Python"]
person_info = {
    "first_name": "Aurora",
    "last_name": "Luna",
    "country": "Indonesia",
    "city": "Palembang",
}

Let us use the print() and len() built-in functions. The print() function takes an unlimited number of arguments. An argument is a value which we can be passed or put inside the function parenthesis, see the example below.

Example:

print("Hello, World!")  # The text Hello, World! is an argument
print(
    "Hello", ",", "World", "!"
)  # it can take multiple arguments, four arguments have been passed
print(len("Hello, World!"))  # it takes only one argument

Hello, World!
Hello , World !
13

Let us print and also find the length of the variables declared at the top:

Example:

# Printing the values stored in the variables

print("First name:", first_name)
print("First name length:", len(first_name))
print("Last name: ", last_name)
print("Last name length: ", len(last_name))
print("Country: ", country)
print("City: ", city)
print("Age: ", age)
print("Student: ", is_student)
print("Skills: ", skills)
print("Person information: ", person_info)

First name: Aurora
First name length: 6
Last name:  Luna
Last name length:  4
Country:  Indonesia
City:  Palembang
Age:  6
Student:  True
Skills:  ['HTML', 'CSS', 'JS', 'React', 'Python']
Person information:  {'first_name': 'Aurora', 'last_name': 'Luna', 'country': 'Indonesia', 'city': 'Palembang'}

Declaring Multiple Variable in a Line#

Multiple variables can also be declared in one line:

Example:

first_name, last_name, country, age, is_student = (
    "Aurora",
    "Luna",
    "Indonesia",
    6,
    True,
)

print(first_name, last_name, country, age, is_student)
print("First name:", first_name)
print("Last name: ", last_name)
print("Country: ", country)
print("Age: ", age)
print("Student: ", is_student)

Aurora Luna Indonesia 6 True
First name: Aurora
Last name:  Luna
Country:  Indonesia
Age:  6
Student:  True

Getting user input using the input() built-in function. Let us assign the data we get from a user into first_name and age variables.

Example:

first_name = input("What is your name: ")
age = input("How old are you? ")

print(first_name)
print(age)

Aurora
6
Contents