RASPBERRY PI: Step-By-Step Guide To Mastering Raspberry PI 3 Hardware And Software (Raspberry Pi 3, Raspberry Pi Programming, Python Programming, C Programming) by Richard Ray

Author:Richard Ray [Ray, Richard]
Language: eng
Format: epub, azw3
Publisher: UNKNOWN
Published: 2017-09-05T21:00:00+00:00

Chapter 8

Python Programming for Raspberry Pi

What you will learn in this chapter

 Start programming with python

 Using python for automation

 Drive the hardware with python

What you will need for this chapter

 Raspberry Pi Board

 Resistors, LEDs

Introduction to Python Programming

In this part of this chapter you will learn how to use python to develop some basic encryption, user input, and creating graphical user interface

Let’s start with the hello world example as in any programming language

Create file named hello.py using nano text editor

Nano –c hello.py

Within the file write the following code

#/usr/bin/python3

#hello.py

Print (“Hello World”)

After writing the code, save and exit. You can run the file using the following command

Python3 hello.py

You should know more about strings if you want to start with python A string is a sequence of characters stored together as a value. We will write code to get the user’s input, using string manipulation to switch the letters and then print encrypted message of the user input. You can maybe use text editors that can be directly on your Raspberry Pi or via VNC or SSH. There are many text editors you can choose from

● nano: You can work with this editor from the terminal

● IDLE3: This editor includes the syntax highlighting, context help, but this program requires x-windwos or x11 to run remotely we will use python3, so make sure that you run IDL3 not IDLE

●Geany: this editor is an Integrated Development Environment (IDE) that supports many programming languages, syntax highlighting, auto completion and very easy code navigation. This is a rich editor , but not for beginners and It will be slow on the Raspberry Pi. If you want to install Geany, write the following command

Sudo apt-get install Geany

To make sure that the Geany editor use python3:

Click on the Execute button to run the code

, you will need to change the build commands. Load the file

And click build and set build commands and then change python to python3

Let’s cerate the program

#/usr/bin/python3

#ecryptionprogram.py

#takes the input and encrypt it

def encrpytText(input_text,key);

output=””

for letter in input_text:

#Ascii Uppercase 65-90 lowercase 97 -122

Ascii_val = ord(letter)

#now write the following code to exclude non characters from encryption

If(ord(“A”) > Ascii_val) or (Ascii_val > ord(“Z”)):

Output+=letter

Else:

#write this code to apply the encryption key

Key_val = Ascii_val + key

#make sure that we use A-Z regardless of key

If not((or(“A”)) < key_val < or(“Z”)):

Key_val = ord(“A”) + (key_val-ord(“A”))\

%(ord(“Z”) –ord(“A”)+1)

#add the encrypted letter to the output

Output+=str(chr(key_val))

Return output

#Test

Def main() Print (“please enter any text to encrypt”)

#get user input

Try:

Us_input = input();

Sc_result = ecryptText(us_input, 10)

Print (“output: ”, sc_result)

Print(“to un-scramble , pls press enter”)

Input()

Un_result = ecryptText(Sc_result, -10)

Print (“output: ” + un_result)

Except UnicodeDecodeError:

Print (“this program supports ASCII characters only”)

Main()

#end of the program The preceding code implements a basic method to encode the text using character substitution called the Caesar Cipher. Named after the emperor Julius Caesar, who used this method to send his secret orders to the army

We have defined two functions, encryptText() and main(). Also when the code is running, the main function contains the user’s input using input() command. The result is stored as a string int the us_ input

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