Data Types and Variables

Contents

Data Types and Variables#

Python as a calculator#

You can use Python to make calculations like addition, subtraction, multiplication, and division.

1 + 1

3 * 4

21 / 7

3.0

10 - 9

Data Types#

Python interprets all data as a type of data. For example, a number is interpreted as an “integer,” and any characters contained within quotes are interpreted as a “string.”

type(1)

int

type('hello world!')

str

type("1")

str

type(1)

int

type(1.)

float

type(True)

bool

type(False)

bool

type(['sausage', 'egg', 'cheese'])

list

type([1, 4, 2])

list

Variables#

Python saves data as “variables,” which are a kind of label that we can assign to values like integers, strings, or lists.

x = 5

y = 10

x + 5

x = "Hello"

'Hello'

y = " Goodbye"

' Goodbye'

x + y 

'Hello Goodbye'

breakfast = ['kiwis', 'yogurt', 'peanut butter sandwish', 'water']

breakfast

['kiwis', 'yogurt', 'peanut butter sandwish', 'water']

type(breakfast)

list

number = 1000

number

Rules for creating variables#

# variables can start with an underscore or an alphabetic character.  
_5 = "five"

# variables are case sensitive
my_variable = "test"
My_variable = "test again"

My_variable

'test again'

my_variable

'test'

# generally variables cannot start with punctuation
$varialbe = "dollar"

  Cell In[34], line 2
    $varialbe = "dollar"
    ^
SyntaxError: invalid syntax

Objects#

Every time you save some data to a variable, you are creating an “object” in python.

# this creates a string type object
greeting = "Hello World!"

greeting

'Hello World!'

Methods for Objects#

Objects have built-in functionality based on their data type, like strings and lists. In other words, you can do certain things to string-type objects that you cannot with list-type objects.

# certain methods, like upper(), can be used to do things to strings
greeting.upper()

'HELLO WORLD!'

# lower() is another string method
greeting.lower()

'hello world!'

greeting

'Hello World!'

breakfast

['kiwis', 'yogurt', 'peanut butter sandwish', 'water']

# there are also methods for lists, like sort()
breakfast.sort()

breakfast

['kiwis', 'peanut butter sandwish', 'water', 'yogurt']

greeting.sort()

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-9-1405c0c7855b> in <module>
----> 1 greeting.sort()

AttributeError: 'str' object has no attribute 'sort'

# string concatenation is when you add two strings together
"Hello" + "goodbye"

'Hellogoodbye'

# f-string formatting is when you use an "f" and curly brackets {} 
# to tell python that you are going to put code in the string

f"Today for breafast, I ate {breakfast}"

"Today for breafast, I ate ['kiwis', 'peanut butter sandwish', 'water', 'yogurt']"

Homework help#

name = "Filipa"

age = 33

f"my name is {name}, and my age is {age}"

'my name is Filipa, and my age is 33'