Introduction to Python
Data Types and Variables
ICS 3U0
Today’s Agenda
Variables
Declaring and Assigning Variables
Data Types
Strings, Integers and Floating
Numbers
Storage and Variables
In
order to interact with the outside world,
programs have to accept Input. Before
doing this, however, we need to discuss
storage and variables.
If
the computer asks the user for their name,
age, grade, address, or any other
information, it should remember that
information.
is stored in memory. A variable
is a specific location in memory. It is called a
Information
Declaring Variables
When
we declare a variable:
◦a space is reserved in memory for that data
◦a name is reserved to identify that data
◦the type of data stored in the variable is
specified (for example, is this variable
going to be a string or integer)
Once
a name is reserved, you cannot declare
another variable by the same name.
Three Basic Data Types
int
– an integer value is a positive or negative
whole number (..., -3, -2, -1, 0, 1, 2, 3, …)
float/double
– a real number involves decimals,
such as 0.5, 0.33, 10.7. You can also represent
integers as reals, but try to avoid this (-3.0, 4.0)
str
– a string value is a collection of characters,
such as a name, address, or other combinations
of letters and numbers
How to Declare Variables in Python
To
create (or declare) a variable, assign it a value.
>>> number = 42
The
equals sign, =, is called the assignment operator, since it is
used to assign a value to a variable.
We
can now refer to the variable by its name, anytime we want.
For example, to check its current value, type the variable’s
name.
>>> number 42
42
Example - Integers
What does the
type function do?
a = 8
b = 6-7
print(a, b)
print("The value of a is:", a)
print("The value of b is:", b)
print(type(a))
print(type(b))
Example - Floating Numbers
a = 8/3
b = 6-7/9
print(a, b)
print("The value of a is:", a)
print("The value of b is:", b)
print(type(a))
print(type(b))
Example - Strings
a = "Mr. cookit"
b = "LOVES programming"
print(a, b)
print("The value of a is:", a)
print("The value of b is:", b)
print(type(a))
print(type(b))
Naming Variables – The RULES
Variables
should start with a lower case letter.
Variables can start with an upper case letter
or an underscore, but those are special cases
and should not be done on a normal basis.
After
the first lower case letter, the variable
may include uppercase and lowercase letters,
along with numbers and underscores.
Variables may not include spaces.
Naming Variables – More RULES
The
official style guide for Python (yes,
programmers really wrote a book on style)
says that multi-word variable names in
Python should be separated by
underscores.
For example, use ….
hair_style and not hairStyle.
Naming Variables – More RULES
However,
we, like most programmers, will use
“camelCase”. That is, using a capital letter to
distinguish each additional word in a variable.

Variables start with a lower case

Classes start with a capital letter (next year :)
For example, use ….
hairStyle for variable
and HairStyle for a class
Naming Variables – Examples
Either of these are fine with me ... I investigated and
ALOT of Python developers use firstName as
opposed to first_name
Exercises - Variables
Complete Exercise 1.6 – Variables
Complete Exercise 1.6 – Variables Typecasting