Python Variables and Constants

Variable

In programming we store values in variables. The values could be string, number, boolean, etc. Simply a variable holds value in a memory location and give a name to it. That value can later be access with the variable name and used in the program.

Syntax:

>>> variable_name = value

Example

>>> var = 10 # numeric variable
>>> string_variable = "bumble bee" # string variable
>>> is_true = False # boolean variable

Here, varstring_variableis_true all are valid variable names.

Rules of creating variables:

The rules for creating variable is similar to creating identifier. We can use letters, numbers and underscore. We can not use reserved keywords as variables. For example. a, x30, num1, var_one, count_1, remainder_of_value, etc all are valid variable names.

Constant

Constant as the name suggest is an item that holds values but its value can not change. It is similar to variable but it’s value is constant and does not change. We generally make constant in separate file and import them in our program. By convention the constant are created with all upper case, which signifies that it’s a constant.

syntax:

CONSTANT_NAME = value

Example.

Create a python file with name constantvalue.py  and write the following code.

PI = 3.14
GRAVITY = 9.8

Let’s use this constant in our program

from constantvalue import PI, GRAVITY

# Calcuate the area of a circle

area_of_circle = PI * 5 * 5
print("Area:", area_of_circle)

# 1000 kg astroid collision force,F= M*G

astroid_collision_force =  1000* GRAVITY
print("Force:", astroid_collision_force)

Note: we will see the import statement in later exercise.

Output of the program is

Area: 78.5
Force: 9800.0

Literals

Literal is the notation or representation of a fixed value in a programming language. In python we have various literals like numeric literals, string literals,  boolean literals and special literals,.

Example

Numeric literals are of binary, decimal, octal, hexadecimal, Float, and Complex type.

# Numeric Literals

number = 10 # Decimal literal(any number value)

print(b)
print(number)
print(octal_literal)
print(hex_value)

# Float literals
a = 3.5 # Float literals
b = 99.008 #Float literals
b1 = 1.5e3

print("a=",a)
print("b=",b)
print("b1=",b1)

# Complex literal
c = 3+4j # complex literal( has syntax RealPart+(ImaginaryPart)j)
d = 3.5+ 9j # complex literal

print("c=",c)
print("d=",d)

# String literal
e = "a"
f = "PythonSpark.com"
multiple_string= """This is
multi line string."""

print("e=",e)
print("f=",f)
print("multiple_string=",multiple_string)

# boolean literal
g = True
h = False
i = (1==True)

print(g,h,i)

# special literal
j = None # special literal

print("j=",j)

Note: None is considered as special literal it represents no value.

The output of above program is

14
10
168
31
a= 3.5
b= 99.008
b1= 1500.0
c= (3+4j)
d= (3.5+9j)
e= a
f= PythonSpark.com
multiple_string= This is
multi line string.
True False True
j= None