Python Variables and Constants

Python Variables

A variable is a named location used to store data in memory.

For example, create a variable called salary and assign the value 1500:

salary = 1500

In addition, it is possible to replace the value of a variable at any time:

salary = 2000
salary = 1750.99

Fundamental points

• Python does not have a command to declare a variable, because a variable is automatically created the moment you assign it a value.
• Python is a type-inferred language, so you don't have to explicitly define the variable type. The Python interpreter automatically knows the real time of a variable.
• Variables do not need to be declared with a particular type and they can also change type after being set.

Assigning values to Variables in Python

The assignment operator = is used to assign a value to a variable.

For example, assign a value tutorialreference.com to the variable tutorial_website and then print out the value assigned to tutorial_website

tutorial_website = "tutorialreference.com`"
print(tutorial_website)

Changing the value of a variable

The assignment operator = is also used to change a value to a variable.

tutorial_website = "example.com"
print(tutorial_website) # print "example.com"

tutorial_website = "tutorialreference.com"

print(tutorial_website) # print "tutorialreference.com"

Assigning multiple values to multiple variables

If you want to assign different value to multiple variables at once, you can do in this way:

a, b, c = 1, 2.3, "Hello World"
print(a) # print 1
print(b) # print 2.3
print(c) # print "Hello World"

If you want to assign the same value to multiple variables at once, you can do in this way:

x = y = z = "same value"
print (x) # print "same value"
print (y) # print "same value"
print (z) # print "same value"

Constants

A constant is a type of variable whose value cannot be changed.

Declaring and Assigning value to constant in Python

In Python, constants are usually declared and assigned in a module.

Python constants are written in all capital letters and underscores separating the words.

For example, create a new module file called constants.py and declare the following constants:

PI = 3.14
GRAVITY = 9.8
E = 2.718

Then, you just need to import the constants module

import constants

print(constant.PI)		# print 3.14
print(constant.GRAVITY)	# print 9.8
print(constant.E)		# print 2.718

Rules and Naming Convention for Variables and constants

Some suggestions:

• 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

• Constant and variable names are case-sensitive.
• Create a name that makes sense. For example, counter makes more sense than c.
• If you want to create a variable name with two words, use the underscore to separate them. For example:

  my_variable
  positive_counter

• To declare a constant, use capital letters if possible. For example:

  PI
  G
  MASS
  SPEED_OF_LIGHT
  TEMP

• Never use special symbols like !, @, #, $, %, etc.
• Do not start the name of a variable with a digit.