Computing: Introduction to Python
Lesson One
Learning Objective
• To use a textual programming language to solve a variety of
computational problems.
Success Criteria
• To know how to start Python IDLE and run a Python program.
• To use Python to perform calculations.
• To write simple programs that respond to user input.
What Is Python?
Python is a programming language.
It was invented in the 1980s.
It was named after comedy group ‘Monty Python’.
Python is used by:
Python is
Yahoo (maps);
easy to learn.
Google (search engine);
Shopzilla (shopping comparison site);
Battlefield 2, Civilisation 4 (computer games);
Industrial Light and Magic
(in films such as ‘The Phantom Menace’ and ‘The Mummy Returns’);
• NASA;
• Nokia;
• Facebook, and many more.
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•
•
•
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Python is used in many universities to teach programming.
Starting Python
We can use Python IDLE to create and run our Python programs.
IDLE is an acronym of Integrated Development Environment.
An Integrated Development Environment contains all the tools needed to
write, test and run computer programs.
• The window that first
appears when you
start Python IDLE is
called the Interactive
mode window.
Starting Python
• From the Interactive mode window, we can click on the File menu item,
and then select New File.
• This opens a new Script mode window.
Starting Python
• Good practice is to have instances of both Interactive and Script mode
windows open side-by-side, something like this:
Interactive
Script
On the left is the
On the right is
Interactive mode
the Script mode
window.
window.
Starting Python
• The Interactive mode window is easy to identify.
• You will always see >>> at the start of each new line.
Starting Python
Key Term
An Integrated Development Environment contains all the
tools needed to write, test and run computer programs. In
Python we use the acronym IDLE. Other programming
languages sometimes use the shorter acronym IDE for
Integrated Development Environment.
Python IDLE has two modes of running.
The Interactive mode gives immediate feedback to every line of code that
is entered, and is useful for testing ideas and small snippets of code.
The Script mode allows a programmer to type in many lines of Python
code, and then save the code as a single program with a file name. This
file can be saved and run at any time. However, any inputs or outputs of
Python programs will always be shown in the Interactive mode.
Hello World
• Let’s stick with the Interactive mode window for now,
and learn our first Python command: print
• print does exactly what it says: it prints information onto the screen.
• It does not print anything onto a printer.
• There is a long established tradition in computer programming.
The first program that most programmers write is often a
“Hello World” program.
• In the Python Interactive window, type: print(“Hello World”)
and then press the Enter key on your keyboard.
Hello World
• Some important things to notice:
Always remember to use the (brackets) with print.
• We also used “quotes” because we were printing text.
Did you notice the different colours?
• print is purple because IDLE recognises print as a Python command.
• “Hello World” is green because it is a string of text (more on this later).
• The printed output is usually blue.
Try the print command again, but
this time type your own sentences.
For example: print(“Goodbye Monty”)
Cool Calculations
• We can also use the Python print command to help us do calculations.
• The important thing to remember here is that we are dealing with
numbers and not text, therefore we do not use “quotes” as before.
• Try the following print instructions now and see what happens:
Can you make up your own calculations?
Cool Calculations
Let’s look at this example once again:
• Computers often use the * symbol (asterisk) for multiplication.
• Why does Python IDLE give the answer 27? If we add 6 and 3, this
gives us 9. Then multiplying 9 by 7 gives 63, not 27!
• The reason is that Python uses BIDMAS.
Do you remember what BIDMAS means?
• Python knows to multiply the 3 and 7 first, and then add 6 afterwards.
So, 3 * 7 = 21, then we add 6 to 21 giving us 27.
Cool Calculations
Try these last examples, and see if you can figure out what
Python is doing with the numbers:
Cool Calculations
The double-slash // is rounding-down
(or “floored”) division. It divides two
values and rounds down the answer.
The double-asterisk ** here means 5 to
the power of 2.
These last ones are modulo-division.
% gives the remainder of a division
between two values.
E.g. 15 / 2 = 7
remainder 1.
Incredible Inputs
So far we’ve learned:
•
•
•
•
How
How
How
How
to
to
to
to
start Python IDLE.
open and run a Python program.
use the print command.
Phew –
do calculations in Python.
well done!
Computer programs become much more interesting and useful when they
can respond to user input.
Let’s find out how to do this in Python.
Type this code in the Interactive window, and then press the Enter key:
Incredible Inputs
You should have seen something like this:
That’s my name – did
you type in your name?
• input is our next Python command. It waits for the user to type in
something, in this case we are asking the user to type in their name.
• What happens to the name that is typed in?
• Answer: not much at the moment!
• There is something that happens though, we just can’t see it yet…
Incredible Inputs
To understand what’s going on, let’s look back at the Python
code we entered:
• name is a variable. We can think of variables
as like boxes in computer memory.
Each box has a label, and we can store
information in each box.
• In our Python code above, we have created
a new variable with the label: name
• name = input(“What is your name?”)
prints the question “What is your name” on screen,
then waits for the user to type something in.
• Whatever text they type in is then stored in the box
labelled name. Let’s see how this works…
Incredible Inputs
This is what happens when we type in our Python code:
>>> name = input(“What is your name?”)
What is your name? Monty
>>>
“Monty”
Incredible Inputs
One last thing about using print and input…
We can do so much more than just print out someone’s name.
Try out the following code in Python and see what happens:
• Take care with your typing, watch our for the commas and quotes!
You should be able to see something like this:
Incredible Inputs
>>> print(“Hello”, name, “, how are you today?”)
Hello Monty, how are you today?
>>>
“Monty”
Well I’m fine and dandy,
thanks for asking!
Incredible Inputs
Let’s put all of our new knowledge and skills into action.
This time however we will be using the Script mode window:
Interactive
Script
On the left is the
On the right is
Interactive mode
the Script mode
window.
window.
Incredible Inputs
Type the following Python code into the Script mode window:
Incredible Inputs
We’ll need to save our program as follows.
• Click on File
• and then Save As …
• Give your file the name: Greetings.py
Incredible Inputs
To see your program in action, either click the F5 function key,
or click on the Run menu item and then Run Module.
Type in your answers and
see what happens:
Incredible Inputs
This is what happens when we run our Python code:
“Monty”
What is your name?
Monty
“not
How are you today? not bad”
bad at all
What is your favourite food?“chips”
fish and chips
Greetings Monty
I hear that you are feeling not bad at all
Maybe you need tasty fish and chips to eat?
“Monty”
“not bad”
“chips”
name, feeling and
food are variables
Let’s Bring It All Together
Key Term
An Integrated Development Environment contains all the
tools needed to write, test and run computer programs. In
Python we use the acronym IDLE. Other programming
languages sometimes use the shorter acronym IDE for
Integrated Development Environment.
Python IDLE has two modes of running.
The Interactive mode gives immediate feedback to every line of code that
is entered, and is useful for testing ideas and small snippets of code.
The Script mode allows a programmer to type in many lines of Python
code, and then save the code as a single program with a file name. This
file can be saved and run at any time. However, any inputs or outputs of
Python programs will always be shown in the Interactive mode.
Let’s Bring It All Together
Key Term
We can think of variables as like boxes. Each box has a label,
and we can store data (information) in each box. This data
can be either text or numbers, and can vary during the running of
a program. When the program ends, the boxes are emptied of data.
Pause for Thought
Python is a ‘high level language’. This means that it is closer to human
language than it is to ‘machine code’, the language that all computer
processors understand. (Machine code is made up of binary instructions,
lots of ones and zeroes).
In order to convert our Python programs into machine code we use a
translator, which is simply another computer program. In other words, we
need a computer program to translate our computer programs! Thinking of
the chicken and the egg idea, how then did programmers make the first
translators? See if you can find out…
Rate Your Progress
Red Light: you have understood some of the objective
and you will think about it some more later on, perhaps
asking a friend or teacher for help.
Amber Light: you have understood most of the objective
and you are happy with your progress.
Green Light: you feel fully confident with this objective
and you understand it well.
Success Criteria:
• To know how to start Python IDLE and run a Python program.
• To use Python to perform calculations.
• To write simple programs that respond to user input.
Nailing It Down
We have learned a lot today about Python IDLE, print and input.
Python is a great programming language to learn.
You can download it yourself at home for free by visiting:
https://www.python.org/downloads/
(or just search for ‘python’ using your favourite search engine).
There are also lots of free online versions of Python which are great for
learning how to code. Try out some of these links now:
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https://snakify.org/
http://pythontutor.com/
https://hourofpython.com/
https://repl.it/languages/python3