(r2) IntroductionToPython < AFNOG

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---+ Sensors for !IoT devices … or A virtual world reflecting the real world
<h2 align="center">A 2 day tutorial with hands-on exercises</h2> <h2 align="center">held during AFNOG 2018 in Dakar, Sénégal<br /><br />Uli Raich (uli.raich@gmail.com)</h2>

---+++ 
---+ The Internet

When the Internet was invented it was used for communications between humans

Typical applications where:<br /><br />
   * Email
   * Remote login
   * File transfers

With cheaper and more powerful micro-controllers devices can communicate with each other

or with centralized servers over the network and they can observe their environment

with dedicated sensors.

This is what we call the Internet of Things (!IoT)

---+++ 
---+ Microprocessors

When I started to work on microprocessors in the early 1980’s these were very simple devices

containing just a single CPU and address and data lines + a few control lines to interface

to external memory and I/O interfaces, typically : a serial and a parallel port.<br /><br /><img align="middle" alt="m6800.png" height="98" src="%ATTACHURL%/m6800.png" title="m6800.png" width="225" /><br /><br />The price for the chip was 176 US $.

The development board was sold for 300 US $.

You got 256 bytes of RAM, 2kBytes of EPROM and the serial and parallel port.

Programming was done in assembly language or even straight machine code.

%RED%No Internet!%ENDCOLOR%

---+++ 
---+ An !IoT device today

This year I bought this micro-controller:

<img alt="esp32price.png" height="429" src="%ATTACHURL%/esp32price.png" title="esp32price.png" width="886" />

---+++ 
---+ The specs

<img alt="esp32.png" height="344" src="%ATTACHURL%/esp32.png" title="esp32.png" width="653" />

---+++ 
---+ The Raspberry Pi

… and this is what we are going to use:

<img alt="RASPBERRY-PI-3_sml.jpg" height="602" src="%ATTACHURL%/RASPBERRY-PI-3_sml.jpg" title="RASPBERRY-PI-3_sml.jpg" width="602" />

---+++ 
---+ Official source of information

The Raspberry Pi has been sold at more than 8 million pieces!

The user community is huge and is now increased by another 15 users!

An enormous wealth of information on all sorts of subjects using the Raspberry Pi

can be found on the WEB.

The official site is

https://www.raspberrypi.org

---+++ 
---+ Specs and price

The price (35 US $) of this board is a bit higher but still much less than the m6800 development board.

And this is what you get:

<br /><img alt="broadcom.png" height="414" src="%ATTACHURL%/broadcom.png" title="broadcom.png" width="823" />

---+++ 
---+ Interfaces and software

In addition to the GPIO (General Purpose I/O) you get<br /><br />
   * a serial interface
   * !I2C
   * SPI
very useful to connect external sensors, ADCs or DACs

On the micro SD card (or a memory stick on one of the USB slots) you can install

a full-blown Linux operating system

(for the Windows gurus: there is also a Windows version)

All you need to have a stand alone computer is <br /><br />
   * an HDMI screen
   * a USB keyboard and mouse
---+++ 
---+ Programming

Since we have a full Linux system programming can be done<br /><br />
   * in C or C++
   * Python
   * or any language that Linux supports … and there are many!
---+++ 
---+ Accessing the RPI remotely

Of course we can use the interfaces on the Raspberry Pi to connect a screen,

keyboard and mouse and use it in stand-alone mode

but we can also make use of the PC resources and access it remotely

There are several ways to access the RPI remotely:

Using the VNC server on the Pi you can access it with a remote desktop from the PC

The secure shell (ssh) allows you to get a remote terminal in the Pi

With scp you can copy files back and forth between the Pi and the PC

With nfs you can mount part of the Pi file system into the PC file system tree

and access the PI SD card as if it was a local PC disk.

---+++ 
---+ The remote Desktop

On the remote desktop the screen is replaced by the computer screen of the device

connected to the RPI and the keyboard by this computer's keyboard. The connected computer

acts like a graphics terminal for the RPI.

You see on the computer exactly what you would see on a directly connected screen.

<img alt="remoteDesktop.png" height="368" src="%ATTACHURL%/remoteDesktop.png" title="remoteDesktop.png" width="655" />

---+++ 
---+ ssh

In the case of ssh you have a single terminal window that is connected to a shell on the Pi.

The command is:

ssh userOnPi@piIPaddress

Where piIPaddress can be the Pi’s IP address or host name.

If you specify the -X option you can run X-11 based programs where

the X protocol is run over the ssh connection.

For Windows computers you need PuTTY in conjunction with

an X server (e.g. Xming) to connect to the RPi

---+++ 
---+ ssh(2)

Here you see a screen dump from the PC with a remote terminal that

started an emacs session on the Pi

<img alt="ssh.png" height="390" src="%ATTACHURL%/ssh.png" title="ssh.png" width="694" />

---+++ 
---+ The Cobbler

As we have seen, the Raspberry Pi has a 40 pin connector onto which many interface signals are connected.

We use a flat cable and a “cobbler” to bring these signals onto a bread board

where we can build our own electronic circuits for acquisition or control by the Rpi.

Libraries in C/C++, Java and Python are available easing software access to these signals.

<img alt="cobbler.png" height="120" src="%ATTACHURL%/cobbler.png" title="cobbler.png" width="220" />

---+++ 
---+ Programming the RPi

As already mentioned, the Raspberry Pi can be programmed in

a large number of programming languages.

One of the most fashionable languages is Python.

Python is an interpreted language and code can be entered into a Python interpreter

which executes it immediately. Like this, Python can e.g. be used as a calculator.

It is however also possible to write whole programs (scripts) which the interpreter executes

Want to learn Python? Try the [[https://docs.python.org/2/tutorial/index.html][Python tutorial]]!

We will attempt to learn the language in 2 h!
---+++ 
---+ Running the Interpreter

<img alt="pythonInterpreter.png" height="268" src="%ATTACHURL%/pythonInterpreter.png" title="pythonInterpreter.png" width="828" />

<br />The quit() function exits the interpreter

---+++ 
---+ idle

Instead of running a standard editor like vi or emacs you may want to run

an%BLUE%<b> I</b>%ENDCOLOR%ntegrated%BLUE%<b> D</b>%ENDCOLOR%evelopment %BLUE%<b>E</b>%ENDCOLOR%nvironment (IDE) created specifically for Python instead.

Try _idle_

<img alt="idle.png" height="370" src="%ATTACHURL%/idle.png" title="idle.png" width="659" />

---+++ 
---++ The same thing as a script in idle

Here you see the 2 idle windows.

The top one contains the editor, the second the Python shell

<img alt="pythonScript.png" height="245" src="%ATTACHURL%/pythonScript.png" title="pythonScript.png" width="712" />

<img alt="pythonShell.png" height="247" src="%ATTACHURL%/pythonShell.png" title="pythonShell.png" width="636" />

---+++ 
---+ Running the Program

The script can berun from the Linux command shell with:

_python scriptName_

or we can make it executable and run it like we would run

any compiled C program or any bash script:

<img alt="pythonBash.png" height="450" src="%ATTACHURL%/pythonBash.png" title="pythonBash.png" width="724" />

---+++ 
---+ Very basic Introduction to Python

Assignments look pretty much the same as assignments in other programming languages.

However, in Python you do not need to declare the variables.

The interpreter finds the right type by itself.

Here an example:

<img alt="assignment.png" height="201" src="%ATTACHURL%/assignment.png" title="assignment.png" width="795" />

---+ Strings in Python

Here some string examples:

<img alt="strings.png" height="557" src="%ATTACHURL%/strings.png" title="strings.png" width="748" />

---+++ 
---+ Conditions

We have seen conditions already in the very first example

<img alt="conditions.png" height="128" src="%ATTACHURL%/conditions.png" title="conditions.png" width="921" />

As you can see, there are no braces around the conditional block but it is indented <br /># indicates an comment<br />In addition to the<i> if</i> statement above we have<i> elif</i> and _else_

---+++ 
---+ while loop

Like in other programming languages we have different types of loops.

Here is the example of a while loop which calculates the Fibonnaci series:

<img alt="while.png" height="119" src="%ATTACHURL%/while.png" title="while.png" width="431" />

This program uses multiple assignments a,b are assigned in the same line<br />Again you can see that the block starts with “:” and is indented.

---+++ 
---+ Lists

Python knows a number of compound data structure the most versatile of which is the list

Lists may contain different data types but usually all members of lists have the same type.

Lists have similar properties as strings:<br /><br />
   * define sub-lists
   * get the length of lists
   * concatenate lists
<img alt="lists.png" height="322" src="%ATTACHURL%/lists.png" title="lists.png" width="672" />

---+++ 
---+ More data structures

Lists provide many different functions (methods) to operate on them:

Append, extend, remove, pop, index, count, sort … Have a look at the tutorial for details

The are also further complex data structures which we don’t have the time to go into:<br /><br />
   * tuples
   * sets
   * dictionaries
---+++ 
---+ For loops

Lists are used in for loops. In Python the iterator can be of any type.

Using the range function you can create the same type of for loops we know from C.

Keywords like _continue_ and _break_ have the same meaning.

_pass_ does nothing and is used only where a statement is syntactically needed

<img alt="for.png" height="165" src="%ATTACHURL%/for.png" title="for.png" width="432" />

... and the result:

<img alt="forResult.png" height="106" src="%ATTACHURL%/forResult.png" title="forResult.png" width="180" />

---+++ 
---+ Function Definition

Like in other high level languages you can create functions

and call them later in your program

<img alt="functionDef.png" height="326" src="%ATTACHURL%/functionDef.png" title="functionDef.png" width="558" />

---+++ 
---+ Modules

We may want to keep function definitions in separate files

and use these definitions in several main programs.

In our example of the Fibonacci numbers we can save the definitions in a file called fibo.py

In order to use the definitions we must import them with

_import fibo_

In order to call the functions we have to all the module name:

_fibo.fib(20)_

or if we we want to import a single function:

_from fibo import fib_

_fib(20)_

The module name is found in the variable __name__<i><b><br /></b></i>

---+++ 
---+ Module Example

<img alt="modules.png" height="320" src="%ATTACHURL%/modules.png" title="modules.png" width="610" />

%SLIDESHOWEND%

-- %USERSIG{UliRaich - 2018-04-24}%

---++ Comments

%COMMENT%

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who
jpg	RASPBERRY-PI-3_sml.jpg	r1	manage	300.6 K	2018-04-24 - 17:49	UliRaich
png	assignment.png	r1	manage	15.9 K	2018-04-24 - 19:42	UliRaich
txt	babylon.py.txt	r1	manage	0.3 K	2018-04-24 - 19:15	UliRaich
png	broadcom.png	r1	manage	52.9 K	2018-04-24 - 18:38	UliRaich
png	cabling.png	r1	manage	1315.7 K	2018-04-24 - 20:50	UliRaich
png	cobbler.png	r1	manage	23.8 K	2018-04-24 - 19:10	UliRaich
png	cobblerPinout.png	r1	manage	281.5 K	2018-04-24 - 20:50	UliRaich
png	conditions.png	r1	manage	19.3 K	2018-04-24 - 19:47	UliRaich
txt	conditions.py.txt	r1	manage	0.3 K	2018-04-24 - 19:15	UliRaich
png	esp32.png	r1	manage	109.8 K	2018-04-24 - 17:53	UliRaich
png	esp32price.png	r1	manage	172.0 K	2018-04-24 - 17:49	UliRaich
txt	fib1.py.txt	r1	manage	0.4 K	2018-04-24 - 19:15	UliRaich
png	files.png	r1	manage	27.1 K	2018-04-24 - 20:50	UliRaich
png	for.png	r1	manage	12.2 K	2018-04-24 - 20:06	UliRaich
txt	forLoop.py.txt	r1	manage	0.2 K	2018-04-24 - 19:15	UliRaich
png	forResult.png	r1	manage	3.4 K	2018-04-24 - 20:06	UliRaich
png	functionDef.png	r1	manage	24.4 K	2018-04-24 - 20:09	UliRaich
png	idle.png	r1	manage	317.8 K	2018-04-24 - 19:31	UliRaich
png	lists.png	r1	manage	35.0 K	2018-04-24 - 19:54	UliRaich
png	m6800.png	r1	manage	26.3 K	2018-04-24 - 17:49	UliRaich
png	moduleCall.png	r1	manage	13.0 K	2018-04-24 - 20:50	UliRaich
png	moduleCallResult.png	r1	manage	17.3 K	2018-04-24 - 20:50	UliRaich
png	moduleRun.png	r1	manage	14.2 K	2018-04-24 - 20:50	UliRaich
png	modules.png	r1	manage	30.8 K	2018-04-24 - 20:14	UliRaich
png	pythonBash.png	r1	manage	108.7 K	2018-04-24 - 19:42	UliRaich
png	pythonInterpreter.png	r1	manage	38.8 K	2018-04-24 - 19:31	UliRaich
png	pythonScript.png	r1	manage	35.3 K	2018-04-24 - 19:31	UliRaich
png	pythonShell.png	r1	manage	32.4 K	2018-04-24 - 19:31	UliRaich
png	remoteDesktop.png	r1	manage	378.8 K	2018-04-24 - 18:47	UliRaich
txt	simpleForLoop.py.txt	r1	manage	0.2 K	2018-04-24 - 19:15	UliRaich
png	ssh.png	r1	manage	293.5 K	2018-04-24 - 18:47	UliRaich
png	strings.png	r1	manage	77.6 K	2018-04-24 - 19:46	UliRaich
txt	strings.py.txt	r1	manage	1.0 K	2018-04-24 - 19:15	UliRaich
png	while.png	r1	manage	7.6 K	2018-04-24 - 19:54	UliRaich
txt	while.py.txt	r1	manage	0.1 K	2018-04-24 - 19:15	UliRaich

Topic revision: r2 - 2018-04-24 - IsaacArmahMensah