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Python Basics

1.2 Variables

Variables

Variables are containers in which data values can be stored within the computer’s memory. They have a name, which is also referred to as an address. 


This is a box / container.
In variable terms, we can give it a name/address called box.

We can put things in the box. In programming, these things are called data values.

We can assign the data value books into the variable called box.
We use assignment operator  =  to assign the data value to the variable.


After assigning, we will have a box containing books.


By assigning a value into the box (variable), we can use the value multiple times by calling the box (variable), instead of retyping "books" (value).

Examples

 
box = "books"   The string value "books" is assigned to the variable box
block_number = 72 The number value 72 is assigned to (=) the variable block_number 
street_01 = ‘Nanyang Ave’ The string value ‘Nanyang Ave’ is assigned to the variable street_01
myList = ["apples", "bananas", "cherries"] The list of fruits are assigned to the bariable myList.

 Tip!  - It is good practice to choose meaningful / descriptive names that reflect the variable’s content for easier identification when you or someone else revisits your codes. Which variable names would you choose?

  • n = "Anna" or name = "Anna"
  • y = 2020 or year = 2020

Rules when assigning variable names
 

1. Must start with a letter, or the underscore character. 

  • Examples:    school             _company           address

2. Can only contain alpha-numeric characters and underscores.

  • (A to z)     _     (0 to 9)

3. Case-sensitive

  • name, Name and NAME are three different variables

4. Cannot contain hyphens.

5. Cannot start with a number.

6. Cannot use Python reserved words – these mean something in Python

False await else import pass
None break except in raise
True class finally is return
and continue for lambda try
as def from nonlocal while
assert del global not with
async elif if or yield

Try It

1. Create a variable called fruit, and store "apple" into the variable you created and print. 

2. Are you able to print the following? Try it in your IDE. 

  1. 01_street = ‘Drexel Drive’
  2. YEAR = 1995
  3. course_code = "DSE2020"
  4. my-birth-year = 1982

More On Variables