Objects and Variables

• Python syntax specifies some ways to represent different types of data. A data representation in Python is called an “object”.

Type	Object type in Python	Example
Integer number	int	123
Decimal number (floating point)	float	3.14
Logic value	bool	True, False
Text	string	"Hello World!"

Variables

• Variables are names we set to refer to objects.
  • A not-so-good metaphor: variables are containers for objects
  • A better metaphor: objects are houses, variables are addresses of these houses

x = 123  # a variable x that contains the integer value 123
x = x + 1  # x is updated with the value of x + 1, becoming 124...
hello = "Hello World!"  # a variable that contains the string "Hello World!"
is_done = True  # a variable is_done with the logic value True

Objects x variables

• It is very important to differentiate!
• Which of the following are variables and which are objects?

"hello"

hello

132

var_1

truev

True

Variable naming conventions in Python

• They MUST start with a letter or with _ (underline)
• They are case sensitive (‘C’ is different from ‘c’)
• They can’t contain: { ( + - * / \ ; . , ?
• They can’t have names of words already reserved for other purposes in Python:

• What happens if?

True = 123

"Hello" = world

1stcar = 2000