In this tutorial, you will learn about Python variables, constants, literals and the instances in which they are used.

PYTHON VARIABLES

A variable is a named location used to store data in the computer’s memory. It is helpful to think of variables as a container that holds data that can be changed later in the program. What this means can be illustrated with a simple analogy.
Consider a container for collecting specimen of live organisms, say cockroaches. What this simply means is that there will always be activities in the container due to the movement of the cockroaches. Consider filling a different container with sand. What do you think would happen? Answer this yourself.
For an example code,

number = 10

Here, we have created a variable named number. We have assigned the value 10 to the variable.

You can think of variables as a bag to store books in it and that book can be replaced at any time.

number = 10
number = 1.1

Initially, the value of number was 10. Later, it was changed to 1.1.

Note: In Python, we don’t actually assign values to the variables. Instead, Python gives the reference of the object(value) to the variable. This will be clear once we get to the part of Object-Oriented Programming.

Assigning values to Variables in Python

As you can see from the above example, you can use the assignment operator = to assign a value to a variable.

Example 1: Declaring and assigning value to a variable

website = "apple.com"
print(website)

Output

apple.com

In the above program, we assigned a value apple.com to the variable website. Then, we printed out the value assigned to website i.e. apple.com

Note: Python is a type-inferred language, so you don’t have to explicitly define the variable type. It automatically knows that apple.com is a string and declares the website variable as a string.

Example 2: Changing the value of a variable

In the above program, we have assigned apple.com to the website variable initially. Then, the value is changed to facebook.com.

Example 3: Assigning multiple values to multiple variables

a, b, c = 5, 3.2, "Hello"

print (a)
print (b)
print (c)

If we want to assign the same value to multiple variables at once, we can do this as:

x = y = z = "same"

print (x)
print (y)
print (z)

The second program assigns the same string to all the three variables x, y and z.

Now earlier I mentioned that things could be going on in a variable, and here’s an example:

a = 3 + 4

In this example, there’s a computation between 3 and 4 going on. And we can say there are activities going on the the variable ‘a’ above.

Constants

A constant is a type of variable whose value cannot be changed. It is helpful to think of constants as containers that hold information which cannot be changed later.

You can think of constants as a bag to store some books which cannot be replaced once placed inside the bag.

Assigning value to constant in Python

In Python, constants are usually declared and assigned in a module. Here, the module is a new file containing variables, functions, etc which is imported to the main file. Inside the module, constants are written in all capital letters and underscores separating the words.

Example 3: Declaring and assigning value to a constant

Create a constant.py:

PI = 3.14
GRAVITY = 9.8

Create a main.py:

import constant

print(constant.PI)
print(constant.GRAVITY)

Output

3.14
9.8

In the above program, we create a constant.py module file. Then, we assign the constant value to PI and GRAVITY. After that, we create a main.py file and import the constant module. Finally, we print the constant value.

Note: In reality, we don’t use constants in Python. Naming them in all capital letters is a convention to separate them from variables, however, it does not actually prevent reassignment.

Rules and Naming Convention for Variables and constants

1. Constant and variable names should have a combination of letters in lowercase (a to z) or uppercase (A to Z) or digits (0 to 9) or an underscore (_). For example:

   snake_case
   MACRO_CASE
   camelCase
   CapWords

2. Create a name that makes sense. For example, vowel makes more sense than v.
3. If you want to create a variable name having two words, use underscore to separate them. For example:

   my_name
   current_salary

4. Use capital letters possible to declare a constant. For example:

   PI
   G
   MASS
   SPEED_OF_LIGHT
   TEMP

5. Never use special symbols like !, @, #, $, %, etc.
6. Don’t start a variable name with a digit.

Literals

Literal is a raw data given in a variable or constant. In Python, there are various types of literals they are as follows:

Numeric Literals

Numeric Literals are immutable (unchangeable). Numeric literals can belong to 3 different numerical types: Integer, Float, and Complex.

Example 4: How to use Numeric literals in Python?

a = 0b1010 #Binary Literals
b = 100 #Decimal Literal 
c = 0o310 #Octal Literal
d = 0x12c #Hexadecimal Literal

#Float Literal
float_1 = 10.5 
float_2 = 1.5e2

#Complex Literal 
x = 3.14j

print(a, b, c, d)
print(float_1, float_2)
print(x, x.imag, x.real)

Output

10 100 200 300
10.5 150.0
3.14j 3.14 0.0

In the above program,

• We assigned integer literals into different variables. Here, a is binary literal, b is a decimal literal, c is an octal literal and d is a hexadecimal literal.
• When we print the variables, all the literals are converted into decimal values.
• 10.5 and 1.5e2 are floating-point literals. 1.5e2 is expressed with exponential and is equivalent to 1.5 * 10².
• We assigned a complex literal i.e 3.14j in variable x. Then we use imaginary literal (x.imag) and real literal (x.real) to create imaginary and real parts of complex numbers.

String literals

A string literal is a sequence of characters surrounded by quotes. We can use both single, double, or triple quotes for a string. And, a character literal is a single character surrounded by single or double quotes.

Example 7: How to use string literals in Python?

strings = "This is Python"
char = "C"
multiline_str = """This is a multiline string with more than one line code."""
unicode = u"u00dcnicu00f6de"
raw_str = r"raw n string"

print(strings)
print(char)
print(multiline_str)
print(unicode)
print(raw_str)

Output

This is Python
C
This is a multiline string with more than one line code.
Ünicöde
raw n string

In the above program, This is Python is a string literal and C is a character literal.

The value in triple-quotes """ assigned to the multiline_str is a multi-line string literal.

The string u”u00dcnicu00f6de” is a Unicode literal which supports characters other than English. In this case, u00dc represents Ü and u00f6 represents ö.

r”raw n string” is a raw string literal.

Boolean literals

A Boolean literal can have any of the two values: True or False.

Example 8: How to use boolean literals in Python?

x = (1 == True)
y = (1 == False)
a = True + 4
b = False + 10

print("x is", x)
print("y is", y)
print("a:", a)
print("b:", b)

Output

x is True
y is False
a: 5
b: 10

In the above program, we use boolean literal True and False. In Python, True represents the value as 1 and False as 0. The value of x is True because 1 is equal to True. And, the value of y is False because 1 is not equal to False.

Similarly, we can use the True and False in numeric expressions as the value. The value of a is 5 because we add True which has a value of 1 with 4. Similarly, b is 10 because we add the False having value of 0 with 10.

Special literals

Python contains one special literal i.e. None. We use it to specify that the field has not been created.

Example 9: How to use special literals in Python?

drink = "Available"
food = None

def menu(x):
    if x == drink:
        print(drink)
    else:
        print(food)

menu(drink)
menu(food)

Output

Available
None

In the above program, we define a menu function. Inside menu, when we set the argument as drink then, it displays Available. And, when the argument is food, it displays None.

Literal Collections

There are four different literal collections List literals, Tuple literals, Dict literals, and Set literals.

Example 10: How to use literals collections in Python?

fruits = ["apple", "mango", "orange"] #list
numbers = (1, 2, 3) #tuple
alphabets = {'a':'apple', 'b':'ball', 'c':'cat'} #dictionary
vowels = {'a', 'e', 'i' , 'o', 'u'} #set

print(fruits)
print(numbers)
print(alphabets)
print(vowels)

Output

['apple', 'mango', 'orange']
(1, 2, 3)
{'a': 'apple', 'b': 'ball', 'c': 'cat'}
{'e', 'a', 'o', 'i', 'u'}

In the above program, we created a list of fruits, a tuple of numbers, a dictionary dict having values with keys designated to each value and a set of vowels.