Noadswood Science, 2014

To know the basics of Python coding and decoding

Wednesday, April 19, 2023

IDE

Using Komodo Edit (the integrated development environment) we are going to build two basics programs…

To get started follow the usual procedure within Komodo Edit

Open the program Click file new > new from template Choose the Python template Click open

IDE

IDE

IDE

Remember – there are three steps to follow when using an IDE program

Enter the code > Save > Run

print(“Hello, World!”) > save hello.py > run command hello.py

*It is also really important to be careful of spacing and indenting when using Python > for now follow exactly the code shown!

**Classic errors > upper and lower case Print and print; single and double quotes ‘’ and “”; minus and underscore - and _; and different brackets (), [], and {}

Error Busting

Have you copied exactly the code to enter?

Have you spelled everything correctly?

Are there two quote marks (‘) around the expression you want to print

Do you have extra spaces at the beginning of the line?

Have you checked the lines above and below the highlighted lines?

Have you asked someone else to check the code against what was asked?

Are you using the correct programming language?

Turtle

Python can draw code – in the code below we can ask it to draw a circle…

Enter the code below into Python – try and determine what each part does…

from turtle import *pendown()for n in range(24):

forward(10)right(15)

penup()

Turtle

Python can draw code – in the code below we can ask it to draw a circle…

Enter the code below into Python – try and determine what each part does…

from turtle import *pendown()for n in range(24): (range starts a loop)

forward(10)right(15) (turns the turtle clockwise 15o)

penup()

Issue

You may have noticed one significant issue here – as soon as the program is done it closes itself down…

There is a simple script that can be used to keep the information on screen: -

input("\n\nPress the enter key to exit.")

The code above says display the statement “Press the enter key to exit” and if the key is pressed then the program will close

Ghosts

The ghost game highlights some of the things to watch out for when writing programs in Python

The game design is simple… A player must walk through a door (there are three

choices) Behind one of the doors is a ghost If the door chosen doesn’t have a ghost the player

continues to the next door If the door chosen does have a ghost then the game

ends A score is collected for how many doors were passed

before a ghost was encountered

Ghosts

#Ghost Game *name of our program (human language)from random import randintprint('Ghost Game')feeling_brave = True *ensure capitals are usedscore = 0while feeling_brave: ghost_door = randint(1, 3) *this area needs to be indented by 4x spaces print('Three doors ahead...') print('A ghost behind one.') print('Which door do you open?') door = input ('1, 2, or 3?') door_num = int(door) if door_num ==ghost_door: print('GHOST!') feeling_brave = False else: *this area needs to be indented by 4x spaces print('No ghost!') print('You enter the next room.') score = score + 1print('Run away!') *indents need to be removedprint('Game over! You scored' , score)input("\n\nPress the enter key to exit.")

Ghosts

When the game is run you will see the following…

The player must enter a number: 1, 2 or 3

Ghosts

If there is no ghost behind the door then you see “No ghost!”

You then get to continue…

Ghosts

If there is a ghost behind the door then you see “GHOST!”

The game is then over – it will tell you a score achieved (the number of times you went through a door without a ghost behind it)

Decoding

The ghost game displays some of the key features of Python

The code structure is very specific: Python uses spaces at the start of lines to work out which instructions belong together

These spaces are known as indents

For example, the code after while feeling_brave: is indented by four spaces to show it is all part of the main loop

Decoding

Game set up

Main loop

Branching part

Game ending

Decoding – Game Setup

The instructions only run once – at the beginning of the game

They setup the title, variables and the “randint” command (choosing the random number 1-3

Command: randint generates random

numbers

Command: print displays text when the game is run

This resets the score to 0

#Ghost Game is a comment –

this is not shown when

the game is run

Decoding – Main Loop

This loop tells the story and receives the player’s guess – it keeps on going as long as there isn’t a ghost behind the door that is picked

When a ghost appears, the “feeling_brave” variables changes to “False” and the loop stops repeating

Command: randint(1, 3) selects a random number between 1 and 3

Input asks for the player’s

answer

print commands

display the text onscreen

Decoding – Branching Part This program takes a different path depending on whether or not

there was a ghost behind the door that was picked

If there wasn’t a ghost the player’s score is increased by one, but if there was a ghost, the “feeling_brave” variable is set to “False”

This branch runs if there is a ghost

behind the door the player picked

If there is no ghost the player

sees the message “You enter the

next room”

The score increases by one each time

the player enters a room without

meeting a ghost

Decoding – Game Ending

This program takes a different path depending on whether or not there was a ghost behind the door that was picked

If there wasn’t a ghost the player’s score is increased by one, but if there was a ghost, the “feeling_brave” variable is set to “False”

The score is a variable – it will

change depending on how many rooms the

player passes through

Input asks for the enter key to be

typed – the screen will remain open until this is done

print commands

display the text onscreen