​Objectives

• Declare and use variables and constants

• Understand and use the basic data types

​Activity

In REPL, create a new PYTHON project, name it variables

​# put the following in main.py

​name = "your name"

​print(name)

​Variable

• Variable is like a container/box which we can put value/data inside

• ​Each variable can store ONE piece of data only at anytime

​grade = "F3"

• The ​= sign in the above statement is called "assignment", which means we store a value to a variable

Retrieving values

• ​To access the value of variable, simply replace value with the variable name:

# the following will output the value of grade​

print(grade)

​

​Variable naming conventions

• You can give (almost) any name to a variable, but:​

  • Meaningful and relevant

    • ​e.g. class_number, firstname

  • Keep it explanatory but concise

• ​Variable cannot start with number and not containing symbols (except _) or space

  • ​So we use _ to replace space, e.g. average_score

• ​All variables in lowercase letters

  • although capital letter is acceptable, but this is the conventions used by the Python community

​Data Types

• ​Each piece of data has it's "data type"

• ​To help the computer to correctly handle and process data

​String

• ​String means sequence of characters

  • ​Python called "str"

• ​To indicate the data is string, we must put string in a pair of " "

​# inside print, we are actually giving a string # for print to output:

​print("Hello world")

​Numbers

• ​Two major types of numbers:

  • ​Integer - integer is called int in Python

  • ​Real - Python called it float

​Character (Char)

• ​Char is one single character

• ​We use 'x' (pair of single quote) to indicate a value is character

• ​There is NO char in python. Python simply use treat character as string

​Boolean (Logical True/False)

• ​Boolean (bool in Python) consisted of two possible values only

  • ​True

  • ​False (Note: the first letter is capital in Python)