Python Data Types

Starter
Strings
Integers
Floats
Converting Types
Challenges 5 to 12
Checklist
Resources

Introduction

What are strings?

Well you already know, because you’ve already used them! Strings are a data type that can be used to store characters, numbers, symbols – pretty much anything!

myStr = “Hello!”

How do we tell Python that we are creating a string?

Answer

We put the data inside speech marks or inverted commas!

Warning!

Don’t mix your speech marks and inverted commas ( ” and ‘ ) – Python will not like it 🙁

Advantages of strings

Strings can store lots of different types of data, have a look at these different things stored in strings:

Disadvantages

You can’t use maths functions with data stored in a string(see the demo)
Strings can’t be changed – you have to overwrite them with a new string.

Demo

Joining Strings

Key Definition: Concatenation

Joining two or more strings together is known as string concatenation.

You already know how to join strings together, because you already did it in lesson 1!

Have a guess – How do we join strings together?

Answer

We used the + sign!

Example

String Methods

Strings have lots of useful methods that make your life easier when coding. Here are a few…

.capitalize()

This capitalizes the first the character in a string ( if it is a letter)

“Example”

name = “bob”

print(name.capitalize())

Bob

[/python]

.title()

This capitalizes the first the character in a string ( if it is a letter)

“Example”

name = “bob jones”

print(name.title())

Bob Jones

[/python]

.upper()

THIS CAPITALIZES EVERY LETTER IN THE STRING.

“Example”

name = “bob”

print(name.upper())

BOB

[/python]

.lower()

this makes all the letters in the string lower case.

“Example”

name = “bob”

print(name.lower())

bob

[/python]

.count(character)

This counts how many times a character appears in the string.

Example

[python]

name = “bob”

print(name.count(“b”))

[/python]

.find(character)

Finds the position of the first instance of the character in the string. P.s. Python starts counting at zero, not 1!!!

Example

[python]

greeting = “hello”

print(greeting.find(“o”))

[/python]

More methods…

Want to know more methods?

try doing : help(str) in the Interactive Interpreter to find out more string methods.

[/toggle]

Strings can't change

[note title=”Key Definition: Immutable”]

Any data type that cannot change is known as immutable.

[/note]

Strings, like many other data types, cannot be changed once you have created. This means that if you want to change any data stored in a string, you have to overwrite the whole variable with a new variable.

Demo

If you are looking to store whole numbers ( positive or negative) then you will probably usually want to store in them in the integer data type. Doing this is easy, in fact you have already done this!

myInt = 55

Answer

You don’t need to put the number in anything! e.g.

[python]

x = 5

[/python]

Once a number is stored in an integer, you can use any of the maths functions you would normally use.

Example

[python]

x = 5

y = 7

z = x * y

print(z)

[/python]

If you want to store a data that contains a decimal place, such as math Pi, then you should normally use a float.

myFlt = 3.412

Answer

Just type the number, including the decimal place.

[python title=”Example”]

pi = 3.142

type(pi)

[/python]

Floats are useful when you are doing calculations that require a higher level of accuracy in calculations.

[note title=”Clever Python 🙂 “]

Python 3 will automatically create a float when you need one.

[python]

x = 3

y = 2

z = x/y

1.5

type(z)

[/python]

[/note]

int(value) - Convert to integer

Key Definition: Type Casting

Sometimes you will need to convert between data that is stored in different types. Python has in-built functions to do this for you.
Converting data from one type to another is known as Type Casting. Programmers often don’t bother using this term but examiners love testing students on obscure vocabulary!

myInt = int(“45”)

[python]

x = “5”

type(x)

x= int(x)

type(x)

[/python]

Used for: