Introduction to Python Things You Need to Know

Introduction to Python – things you need to know

1. Open Python from the ICT menu

2. You want the Python GUI which has a white background. If it is black close and try again.

3. This is for creating text based coded programs and the name comes from the Monty Python series. The Python GUI (graphical user interface or gooey) is called the Python shell when it opens up. This is a word processing program that you will use to code in.

4. As soon as you hit the enter key it will run the program and you do not want it to do that as you may want to open several lines of code. This is a pain so you have to find a way to stop it doing this…

5. Click file new then file save as and set up a Python folder to keep all your programs (and you will make lots). It will open a new window – in this window you can type lines of code and it will not run your program or try to do anything with it until you hit F5.

6. Do this every time you start a new program: 1) open Python GUI, 2) File save as name the program before you start. 1 Your First Program

1. Type this into Python

2. Run the program in F5 it will prompt you to save – call it prog1

The word print will come up in purple which means it is a COMMAND

The Hello world will come up in green which means it is a TEXT STRING

STRINGS need speech marks so the computer knows it is a string and not a command. (How do we know when someone is staff? Maybe they wear a top that says staff so we can identify them. It’s the same with code we use “” as identifying marks so the computer program recognises that you want that to be seen as a text string.)

Brackets will be black which means they are a variable – more on that later. Exercise 1a

Change the program so that it says “pleased to meet you” Exercise 1b

Change the program so it says “This is Lucy’s first program” but change the name to yours.

2 Using syntax Syntax is how we describe the way the words are arranged on the page. Sometimes you might not want all the words to run from left to right, you may want line breaks.

1. Type the following into Python:

2. Press F5 and call it prog2

Exercise 2a

Sometimes we want a space between lines that print out. Try this code:

New vocab: syntax

3 Variables We can assign or store data in a variable so that it can be used in the program. For example we may tell the computer that x=6 or that a=3 and we can assign names as a string variable.

The first line tells the computer that name is a variable – in this case a text string. In that text string is the name Sarah. The second line then tells the computer to print the word hello and whatever is in the name variable. This is very handy with really long bits of code that you don’t want to type over and over again – you can pop it into a variable and call it up every time you need it. Handy eh?

Note the syntax that the second line has a space after the hello. Without the space it just runs the two words together helloSarah. Exercise 3a

Type this program and run it – what does it do?

4 Annotations As you move along your program writing it you may wish to add some annotations so you know what you were thinking or what the program was trying to do. This will help you when you are writing a longer program.

#we use a hashtag symbol to indicate that we are annotating our own work and it should appear in red.

If you want to type more than this it will just keep typing across the page and will not move down like a normal word processing program will do. So to stop it being strange like that we can use three “”” speech marks to make a block of text in an annotation.

5 Interactive

programing

A TV programme is not the same as a computer program or programing. The spelling is different. Just thought we should mention this at this stage. Anyway coding is creating programs for other people to use. There are two people in this relationship:

So let’s make a program for someone else to use. First decide in the class who will be your user. Now you can create some code for them and when you have finished ask them to try out your program to see if it works.

Did your user try your program?

Did it work? If it didn’t work look carefully at the spacing (syntax) you may be putting too many spaces in. Coding is like learning to type in a different way all over again. Exercise 5a

Now code a program to ask what their favourite kind of music is and to output that you really like that kind of music too.

6 Calculations with variables

Python also can carry out calculations using arithmetic operator symbols that you would find in a maths lesson or on Excel. + (plus) – (minus) / (divide) * (multiply)

Try this simple program

Python will do the maths for you, impressive eh?. We can now use operators and variables in the same program:

Notice that everything you want printed will need to be in brackets. That is so the program knows what to do with it. Exercise 6a

Create a program where a=10 b=7 and x=17

7 Using the Python libraries Python has a group of libraries of information that you can call on to help with your calculations. For example it has a maths (or math) library which contains values such as pi so you so not have to put it in.

Open Python IDE

Click on Help>open Python Docs > Left hand bar open Python Standard Library You can scroll through and see all the libraries

To call a library we use an import math, note in the program below that a would be radius of a circle and the surface area formula is π r2. To get a square we use two stars, and we use the variable a to stand in for r. So the finished formula looks like this; pi*a**2

We can round the result to 3 decimal places by adding the code to the above program:

C = round(pi*a**2,3)

8 The IF statement A CONSTRUCT is an item of programming like a loop, it is a chunk of code which does something. The IF statement is a construct.

The IF statement can be Boolean which means that it is either true or false.

So in programming:

== means is equal to

!= means is not equal to

Create the following program, the indents are important for how the computer organises the program. Some of the indents it will put in correctly some you will need to force with tab key.

You can only run this program once, each time try typing different letters and resetting and running the program each time.

Exercise 8a

Now try re-writing the program so that if orange is typed a funny joke appears and if banana is typed it gives a warning message. 9 Using the random module from the library

The library in Python as well as having math also has a random number generator which you can use in a number of programs. So have a go at calling up the random module from the library.

First code a dice:

Now expand this program:

To get the dice to roll again we will need to create a loop and that comes later. 9 continued using the random library

We can use the random to give us a different random number every time – ideal if you are coding a game that needs a random outcome each time or trying to pick numbers from a hat.

#First we import the random library into the program

Import random

#Then we identify our variable and how this should relate to the random library, the randint just means it’s a random integer rather than a fraction or decimal

X=random.randint(1,100)

#Then we request that the program prints out the variable – which if we have done it right should be a random number from 1 to a 100

Print (x)

Exercise 9a

Can you code the above program? 9 continued - Longer random program – magic 8 ball…

A magic 8 ball is a toy that you can shake and it will give a random answer to a question. Answers include; yes, no, maybe, go for it! You can edit this as you code. 10 Iteration

Iteration is another coding terminology that means repeat. You may have heard someone say “I will reiterate what I said earlier about not leaving your folders….” This means they are repeating what they said at an earlier point in time.

Let’s look at a simple iteration code – make sure your indents are right (see the big arrow)

Why does the program keep going forever? How often does x meet the condition x<5, if this is always the case then the program will continue to run until you kill it. Exercise 10 a

Fix the program, by adding the following code; x=x+1, print(“finished”) Exercise 10 b challenge

Write a program to ask for a password, and when the word apple is input then it should say that the password is accepted. Exercise 10 c Dragon Realm Game import random import time def displayIntro(): print('You are in a land full of dragons. In front of you,') print('you see two caves. In one cave, the dragon is friendly') print('and will share his treasure with you. The other dragon') print('is greedy and hungry, and will eat you on sight.') print() def chooseCave(): cave = '' while cave != '1' and cave != '2': print('Which cave will you go into? (1 or 2)') cave = input() return cave def checkCave(chosenCave): print('You approach the cave...') time.sleep(2) print('It is dark and spooky...') time.sleep(2) print('A large dragon jumps out in front of you! He opens his jaws and...') print() time.sleep(2) friendlyCave = random.randint(1, 2)

if chosenCave == str(friendlyCave): print('Gives you his treasure!') else: print('Gobbles you down in one bite!') playAgain = 'yes' while playAgain == 'yes' or playAgain == 'y':

displayIntro() caveNumber = chooseCave() checkCave(caveNumber) print('Do you want to play again? (yes or no)') playAgain = input()