Raspberry Pi OS
Introduction
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Raspberry Pi OS is a free operating system based on Debian, optimised for the Raspberry Pi hardware, and is the recommended operating system for normal use on a Raspberry Pi. The OS comes with over 35,000 packages: pre-compiled software bundled in a nice format for easy installation on your Raspberry Pi.
Raspberry Pi OS is under active development, with an emphasis on improving the stability and performance of as many Debian packages as possible on Raspberry Pi.
Updating and Upgrading Raspberry Pi OS
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It’s important to keep your Raspberry Pi up to date. The first and probably the most important reason is security. A device running Raspberry Pi OS contains millions of lines of code that you rely on. Over time, these millions of lines of code will expose well-known vulnerabilities, which are documented in publicly available databases meaning that they are easy to exploit. The only way to mitigate these exploits as a user of Raspberry Pi OS is to keep your software up to date, as the upstream repositories track CVEs closely and try to mitigate them quickly.
The second reason, related to the first, is that the software you are running on your device most certainly contains bugs. Some bugs are CVEs, but bugs could also be affecting the desired functionality without being related to security. By keeping your software up to date, you are lowering the chances of hitting these bugs.
Using APT
The easiest way to manage installing, upgrading, and removing software is using APT (Advanced Packaging Tool) from Debian. To update software in Raspberry Pi OS, you can use the apt
tool from a Terminal window.
Keeping your Operating System up to Date
APT keeps a list of software sources on your Raspberry Pi in a file at /etc/apt/sources.list
. Before installing software, you should update your package list with apt update
. Go ahead and open a Terminal window and type:
sudo apt update
Next, upgrade all your installed packages to their latest versions with the following command:
sudo apt full-upgrade
Note that full-upgrade
is used in preference to a simple upgrade
, as it also picks up any dependency changes that may have been made.
Generally speaking, doing this regularly will keep your installation up to date for the particular major Raspberry Pi OS release you are using (e.g. Buster). It will not update from one major release to another, for example, Stretch to Buster or Buster to Bullseye.
However, there are occasional changes made in the Raspberry Pi OS image that require manual intervention, for example a newly introduced package. These are not installed with an upgrade, as this command only updates the packages you already have installed.
Note
|
The kernel and firmware are installed as a Debian package, and so will also get updates when using the procedure above. These packages are updated infrequently and after extensive testing. |
If moving an existing SD card to a new Raspberry Pi model (for example the Raspberry Pi Zero 2 W), you may also need to update the kernel and the firmware first using the instructions above.
Running Out of Space
When running sudo apt full-upgrade
, it will show how much data will be downloaded and how much space it will take up on the SD card. It’s worth checking with df -h
that you have enough free disk space, as unfortunately apt
will not do this for you. Also be aware that downloaded package files (.deb
files) are kept in /var/cache/apt/archives
. You can remove these in order to free up space with sudo apt clean
(sudo apt-get clean
in older releases of apt).
Upgrading from Previous Operating System Versions
Warning
|
Upgrading an existing image is possible, but is not guaranteed to work in every circumstance and we do not recommend it. If you do wish to try upgrading your operating system version, we strongly suggest making a backup first — we can accept no responsibility for loss of data from a failed update. |
The latest version of Raspberry Pi OS is based on Debian Bullseye. The previous version was based on Buster. If you want to perform an in-place upgrade from Buster to Bullseye (and you’re aware of the risks) see the instructions in the forums.
Searching for Software
You can search the archives for a package with a given keyword with apt-cache search
:
apt-cache search locomotive
sl - Correct you if you type `sl' by mistake
You can view more information about a package before installing it with apt-cache show
:
apt-cache show sl
Package: sl
Version: 3.03-17
Architecture: armhf
Maintainer: Hiroyuki Yamamoto <yama1066@gmail.com>
Installed-Size: 114
Depends: libc6 (>= 2.4), libncurses5 (>= 5.5-5~), libtinfo5
Homepage: http://www.tkl.iis.u-tokyo.ac.jp/~toyoda/index_e.html
Priority: optional
Section: games
Filename: pool/main/s/sl/sl_3.03-17_armhf.deb
Size: 26246
SHA256: 42dea9d7c618af8fe9f3c810b3d551102832bf217a5bcdba310f119f62117dfb
SHA1: b08039acccecd721fc3e6faf264fe59e56118e74
MD5sum: 450b21cc998dc9026313f72b4bd9807b
Description: Correct you if you type `sl' by mistake
Sl is a program that can display animations aimed to correct you
if you type 'sl' by mistake.
SL stands for Steam Locomotive.
Installing a Package with APT
sudo apt install tree
Typing this command should inform the user how much disk space the package will take up and asks for confirmation of the package installation. Entering Y
(or just pressing Enter
, as yes is the default action) will allow the installation to occur. This can be bypassed by adding the -y
flag to the command:
sudo apt install tree -y
Installing this package makes tree
available for the user.
Uninstalling a Package with APT
You can uninstall a package with apt remove
:
sudo apt remove tree
The user is prompted to confirm the removal. Again, the -y
flag will auto-confirm.
You can also choose to completely remove the package and its associated configuration files with apt purge
:
sudo apt purge tree
Using rpi-update
rpi-update
is a command line application that will update your Raspberry Pi OS kernel and VideoCore firmware to the latest pre-release versions.
Warning
|
Pre-release versions of software are not guaranteed to work. You should not use rpi-update on any system unless recommended to do so by a Raspberry Pi engineer. It may leave your system unreliable or even completely broken. It should not be used as part of any regular update process.
|
The rpi-update
script was originally written by Hexxeh, but is now supported by Raspberry Pi engineers. The script source is in the rpi-update repository.
What it does
rpi-update
will download the latest pre-release version of the linux kernel, its matching modules, device tree files, along with the latest versions of the VideoCore firmware. It will then install these files to relevant locations on the SD card, overwriting any previous versions.
All the source data used by rpi-update
comes from the rpi-firmware repository. This repository simply contains a subset of the data from the official firmware repository, as not all the data from that repo is required.
Running rpi-update
If you are sure that you need to use rpi-update
, it is advisable to take a backup of your current system first as running rpi-update
could result in a non-booting system.
rpi-update
needs to be run as root. Once the update is complete you will need to reboot.
sudo rpi-update sudo reboot
It has a number of options documented in the rpi-update repository.
How to get back to safety
If you have done an rpi-update
and things are not working as you wish, if your Raspberry Pi is still bootable you can return to the stable release using:
sudo apt-get update sudo apt install --reinstall libraspberrypi0 libraspberrypi-{bin,dev,doc} raspberrypi-bootloader raspberrypi-kernel
You will need to reboot your Raspberry Pi for these changes to take effect.
Playing Audio and Video
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Warning
|
The following documentation refers to Raspberry Pi OS Buster and earlier versions. OMXPlayer has been deprecated in the latest OS release. If you are running Bullseye, VLC is now the recommended alternative. |
The simplest way of playing audio and video on Raspberry Pi is to use the installed OMXPlayer application.
This is hardware accelerated, and can play back many popular audio and video file formats. OMXPlayer uses the OpenMAX (omx
) hardware acceleration interface (API) which is the officially supported media API on Raspberry Pi. OMXPlayer was developed by the Kodi Project’s Edgar Hucek.
The OMXPlayer Application
The simplest command line is omxplayer <name of media file>
. The media file can be audio or video or both. For the examples below, we used an H264 video file that is included with the standard Raspberry Pi OS installation.
omxplayer /opt/vc/src/hello_pi/hello_video/test.h264
By default the audio is sent to the analog port. If you are using a HDMI-equipped display device with speakers, you need to tell omxplayer to send the audio signal over the HDMI link.
omxplayer --adev hdmi /opt/vc/src/hello_pi/hello_video/test.h264
When displaying video, the whole display will be used as output. You can specify which part of the display you want the video to be on using the window option.
omxplayer --win 0,0,640,480 /opt/vc/src/hello_pi/hello_video/test.h264
You can also specify which part of the video you want to be displayed: this is called a crop window. This portion of the video will be scaled up to match the display, unless you also use the window option.
omxplayer --crop 100,100,300,300 /opt/vc/src/hello_pi/hello_video/test.h264
If you are using the Raspberry Pi Touch Display, and you want to use it for video output, use the display option to specify which display to use. n
is 5 for HDMI, 4 for the touchscreen. With the Raspberry Pi 4 you have two options for HDMI output. n
is 2 for HDMI0 and 7 for HDMI1.
omxplayer --display n /opt/vc/src/hello_pi/hello_video/test.h264
How to Play Audio
To play an MP3 file, navigate to the location of the .mp3
file in the terminal using cd
and then type the following command:
omxplayer example.mp3
This will play the audio file example.mp3
through either your monitor’s built-in speakers or your headphones, connected via the headphone jack.
If you need an example file you can download one from here using the following command:
wget https://raw.githubusercontent.com/raspberrypilearning/burping-jelly-baby/master/data/la.mp3 -O example.mp3 --no-check-certificate
If you cannot hear anything, make sure your headphones or speakers are connected correctly. Note that omxplayer doesn’t use ALSA and so ignores the audio configuration set by raspi-config
or amixer
.
If omxplayer’s auto-detection of the correct audio output device fails, you can force output over HDMI with:
omxplayer -o hdmi example.mp3
Alternatively, you can force output over the headphone jack with:
omxplayer -o local example.mp3
You can even force output over both the headphone jack and HDMI with:
omxplayer -o both example.mp3
How to Play Video
To play a video, navigate to the location of your video file in the terminal using cd
, then type the following command:
omxplayer example.mp4
This will play the example.mp4
in full screen. Hit Ctrl + C
to exit.
On the Raspberry Pi 4, hardware support for MPEG2 and VC-1 codecs has been removed, so we recommend the use of the VLC application, which supports these formats in software. In addition, VLC has hardware support for H264 and the new HEVC codec.
An Example Video
A video sample of the animated film Big Buck Bunny is available on your Raspberry Pi. To play it enter the following command into a terminal window:
omxplayer /opt/vc/src/hello_pi/hello_video/test.h264
On a Raspberry Pi 4, use the following command for H264 files:
omxplayer /opt/vc/src/hello_pi/hello_video/test.h264
or for H264, VC1, or MPEG2
vlc /opt/vc/src/hello_pi/hello_video/test.h264
When using VLC, you can improve playback performance by encapsulating the raw H264 stream, for example from the Raspberry Pi Camera Module. This is easily done using ffmpeg
. Playback is also improved if VLC is run full screen; either select fullscreen from the user interface, or you can add the --fullscreen
options to the vlc
command line.
This example command converts video.h264
to a containerised video.mp4
at 30 fps:
ffmpeg -r 30 -i video.h264 -c:v copy video.mp4
Options During Playback
There are a number of options available during playback, actioned by pressing the appropriate key. Not all options will be available on all files. The list of key bindings can be displayed using omxplayer --keys
:
1 decrease speed 2 increase speed < rewind > fast forward z show info j previous audio stream k next audio stream i previous chapter o next chapter n previous subtitle stream m next subtitle stream s toggle subtitles w show subtitles x hide subtitles d decrease subtitle delay (- 250 ms) f increase subtitle delay (+ 250 ms) q exit omxplayer p / space pause/resume - decrease volume + / = increase volume left arrow seek -30 seconds right arrow seek +30 seconds down arrow seek -600 seconds up arrow seek +600 seconds
Playing in the Background
omxplayer
will close immediately if run in the background without tty (user input), so to run successfully, you need to tell omxplayer
not to require any user input using the --no-keys
option.
omxplayer --no-keys example.mp3 &
Adding the &
at the end of the command runs the job in the background. You can then check the status of this background job using the jobs
command. By default, the job will complete when omxplayer
finishes playing, but if necessary, you can stop it at any point using the kill
command.
$ jobs
[1]- Running omxplayer --no-keys example.mp3 &
$ kill %1
$
[1]- Terminated omxplayer --no-keys example.mp3 &
Using a USB webcam
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Rather than using the Raspberry Pi camera module, you can use a standard USB webcam to take pictures and video on your Raspberry Pi.
Note
|
The quality and configurability of the camera module is highly superior to a standard USB webcam. |
First, install the fswebcam
package:
sudo apt install fswebcam
If you are not using the default pi
user account, you need to add your username to the video
group, otherwise you will see 'permission denied' errors.
sudo usermod -a -G video <username>
To check that the user has been added to the group correctly, use the groups
command.
Basic Usage
Enter the command fswebcam
followed by a filename and a picture will be taken using the webcam, and saved to the filename specified:
fswebcam image.jpg
This command will show the following information:
--- Opening /dev/video0... Trying source module v4l2... /dev/video0 opened. No input was specified, using the first. Adjusting resolution from 384x288 to 352x288. --- Capturing frame... Corrupt JPEG data: 2 extraneous bytes before marker 0xd4 Captured frame in 0.00 seconds. --- Processing captured image... Writing JPEG image to 'image.jpg'.

Note
|
The small default resolution used, and the presence of a banner showing the timestamp. |
The webcam used in this example has a resolution of 1280 x 720
so to specify the resolution I want the image to be taken at, use the -r
flag:
fswebcam -r 1280x720 image2.jpg
This command will show the following information:
--- Opening /dev/video0... Trying source module v4l2... /dev/video0 opened. No input was specified, using the first. --- Capturing frame... Corrupt JPEG data: 1 extraneous bytes before marker 0xd5 Captured frame in 0.00 seconds. --- Processing captured image... Writing JPEG image to 'image2.jpg'.

Picture now taken at the full resolution of the webcam, with the banner present.
Removing the Banner
Now add the --no-banner
flag:
fswebcam -r 1280x720 --no-banner image3.jpg
which shows the following information:
--- Opening /dev/video0... Trying source module v4l2... /dev/video0 opened. No input was specified, using the first. --- Capturing frame... Corrupt JPEG data: 2 extraneous bytes before marker 0xd6 Captured frame in 0.00 seconds. --- Processing captured image... Disabling banner. Writing JPEG image to 'image3.jpg'.

Now the picture is taken at full resolution with no banner.
Automating Image Capture
You can write a Bash script which takes a picture with the webcam. The script below saves the images in the /home/pi/webcam
directory, so create the webcam
subdirectory first with:
mkdir webcam
To create a script, open up your editor of choice and write the following example code:
#!/bin/bash
DATE=$(date +"%Y-%m-%d_%H%M")
fswebcam -r 1280x720 --no-banner /home/pi/webcam/$DATE.jpg
This script will take a picture and name the file with a timestamp. Say we saved it as webcam.sh
, we would first make the file executable:
chmod +x webcam.sh
Then run with:
./webcam.sh
Which would run the commands in the file and give the usual output:
--- Opening /dev/video0... Trying source module v4l2... /dev/video0 opened. No input was specified, using the first. --- Capturing frame... Corrupt JPEG data: 2 extraneous bytes before marker 0xd6 Captured frame in 0.00 seconds. --- Processing captured image... Disabling banner. Writing JPEG image to '/home/pi/webcam/2013-06-07_2338.jpg'.
Time-Lapse Captures
You can use cron
to schedule taking a picture at a given interval, such as every minute to capture a time-lapse.
First open the cron table for editing:
crontab -e
This will either ask which editor you would like to use, or open in your default editor. Once you have the file open in an editor, add the following line to schedule taking a picture every minute (referring to the Bash script from above):
* * * * * /home/pi/webcam.sh 2>&1
Save and exit and you should see the message:
crontab: installing new crontab
Ensure your script does not save each picture taken with the same filename. This will overwrite the picture each time.
Useful Utilities
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There are several useful command line
tvservice
tvservice
is a command line application used to get and set information about the display, targeted mainly at HDMI video and audio.
Typing tvservice
by itself will display a list of available command line options.
-o, --off
Powers off the display output.
Note
|
Powering off the output using this command will also destroy any framebuffers/dispmanx layers associated with the display. These are NOT re-established with a subsequent power on, so will result in a blank screen. |
A better option is to use the vcgencmd display_power option, as this will retain any framebuffers, so when the power is turned back on the display will be the returned to the previous power on state.
-e, --explicit="Group Mode Drive"
Power on the HDMI with the specified settings
Group can be one of CEA
, DMT
, CEA_3D_SBS
, CEA_3D_TB
, CEA_3D_FP
, CEA_3D_FS
.
Mode is one of the modes returned from the -m, --modes
option.
Drive can be one of HDMI
, DVI
.
-c, --sdtvon="Mode Aspect [P]"
Power on the SDTV (composite output) with the specified mode, PAL
or NTSC
, and the specified aspect, 4:3
, 14:9
, 16:9
. The optional P
parameter can be used to specify progressive mode.
-m, --modes=Group
where Group is CEA
or DMT
.
Shows a list of display modes available in the specified group.
-s, --status
Shows the current settings for the display mode, including mode, resolution, and frequency.
-a, --audio
Shows the current settings for the audio mode, including channels, sample rate and sample size.
-d, --dumpid=filename
Save the current EDID to the specified filename. You can then use edidparser <filename>
to display the data in a human readable form.
vcgencmd
The vcgencmd
tool is used to output information from the VideoCore GPU on the Raspberry Pi. You can find source code for the vcgencmd
utility on Github.
To get a list of all commands which vcgencmd
supports, use vcgencmd commands
. Some useful commands and their required parameters are listed below.
vcos
The vcos
command has two useful sub-commands:
-
version
displays the build date and version of the firmware on the VideoCore -
log status
displays the error log status of the various VideoCore firmware areas
get_camera
Displays the enabled and detected state of the Raspberry Pi camera: 1
means yes, 0
means no. Whilst all firmware except cutdown versions support the camera, this support needs to be enabled by using raspi-config.
get_throttled
Returns the throttled state of the system. This is a bit-pattern - a bit being set indicates the following meanings:
Bit | Hex value | Meaning |
---|---|---|
0 |
0x1 |
Under-voltage detected |
1 |
0x2 |
Arm frequency capped |
2 |
0x4 |
Currently throttled |
3 |
0x8 |
Soft temperature limit active |
16 |
0x10000 |
Under-voltage has occurred |
17 |
0x20000 |
Arm frequency capping has occurred |
18 |
0x40000 |
Throttling has occurred |
19 |
0x80000 |
Soft temperature limit has occurred |
measure_temp
Returns the temperature of the SoC as measured by its internal temperature sensor;
on Raspberry Pi 4, measure_temp pmic
returns the temperature of the PMIC.
measure_clock [clock]
This returns the current frequency of the specified clock. The options are:
clock | Description |
---|---|
arm |
ARM core(s) |
core |
GPU core |
h264 |
H.264 block |
isp |
Image Sensor Pipeline |
v3d |
3D block |
uart |
UART |
pwm |
PWM block (analogue audio output) |
emmc |
SD card interface |
pixel |
Pixel valves |
vec |
Analogue video encoder |
hdmi |
HDMI |
dpi |
Display Parallel Interface |
e.g. vcgencmd measure_clock arm
measure_volts [block]
Displays the current voltages used by the specific block.
block | Description |
---|---|
core |
VC4 core voltage |
sdram_c |
SDRAM Core Voltage |
sdram_i |
SDRAM I/O voltage |
sdram_p |
SDRAM Phy Voltage |
otp_dump
Displays the content of the OTP (one-time programmable) memory inside the SoC. These are 32-bit values, indexed from 8 to 64. See the OTP bits page for more details.
get_config [configuration item|int|str]
Display value of the configuration setting specified: alternatively, specify either int
(integer) or str
(string) to see all configuration items of the given type. For example:
vcgencmd get_config total_mem
returns the total memory on the device in megabytes.
get_mem type
Reports on the amount of memory addressable by the ARM and the GPU. To show the amount of ARM-addressable memory use vcgencmd get_mem arm
; to show the amount of GPU-addressable memory use vcgencmd get_mem gpu
. Note that on devices with more than 1GB of memory the arm
parameter will always return 1GB minus the gpu
memory value, since the GPU firmware is only aware of the first 1GB of memory. To get an accurate report of the total memory on the device, see the total_mem
configuration item - see get_config
section above.
codec_enabled [type]
Reports whether the specified CODEC type is enabled. Possible options for type are AGIF, FLAC, H263, H264, MJPA, MJPB, MJPG, MPG2, MPG4, MVC0, PCM, THRA, VORB, VP6, VP8, WMV9, WVC1. Those highlighted currently require a paid for licence (see the this config.txt section for more info), except on the Raspberry Pi 4 and 400, where these hardware codecs are disabled in preference to software decoding, which requires no licence. Note that because the H.265 HW block on the Raspberry Pi 4 and 400 is not part of the VideoCore GPU, its status is not accessed via this command.
mem_oom
Displays statistics on any OOM (out of memory) events occurring in the VideoCore memory space.
hdmi_timings
Displays the current HDMI settings timings. See Video Config for details of the values returned.
display_power [0 | 1 | -1] [display]
Show current display power state, or set the display power state. vcgencmd display_power 0
will turn off power to the current display. vcgencmd display_power 1
will turn on power to the display. If no parameter is set, this will display the current power state. The final parameter is an optional display ID, as returned by tvservice -l
or from the table below, which allows a specific display to be turned on or off.
Note that for the 7" Raspberry Pi Touch Display this simply turns the backlight on and off. The touch functionality continues to operate as normal.
vcgencmd display_power 0 7
will turn off power to display ID 7, which is HDMI 1 on a Raspberry Pi 4.
Display | ID |
---|---|
Main LCD |
0 |
Secondary LCD |
1 |
HDMI 0 |
2 |
Composite |
3 |
HDMI 1 |
7 |
To determine if a specific display ID is on or off, use -1 as the first parameter.
vcgencmd display_power -1 7
will return 0 if display ID 7 is off, 1 if display ID 7 is on, or -1 if display ID 7 is in an unknown state, for example undetected.
vcdbg
vcdbg
is an application to help with debugging the VideoCore GPU from Linux running on the ARM. It needs to be run as root. This application is mostly of use to Raspberry Pi engineers, although there are some commands that general users may find useful.
sudo vcdbg help
will give a list of available commands.
Note
|
Only options of use to end users have been listed. |
log
Dumps logs from the specified subsystem. Possible options are:
log | Description |
---|---|
msg |
Prints out the message log |
assert |
Prints out the assertion log |
ex |
Prints out the exception log |
info |
Prints out information from the logging headers |
level |
Sets the VCOS logging level for the specified category, n|e|w|i|t |
list |
List the VCOS logging levels |
e.g. To print out the current contents of the message log:
vcdbg log msg
Python
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Python is a powerful programming language that’s easy to use easy to read and write and, with Raspberry Pi, lets you connect your project to the real world. Python syntax is clean, with an emphasis on readability, and uses standard English keywords.
Thonny
The easiest introduction to Python is through Thonny, a Python 3 development environment. You can open Thonny from the desktop or applications menu.
Thonny gives you a REPL (Read-Evaluate-Print-Loop), which is a prompt you can enter Python commands into. Because it’s a REPL, you even get the output of commands printed to the screen without using print
. In the Thonny application, this is called the Shell window.
You can use variables if you need to but you can even use it like a calculator. For example:
>>> 1 + 2
3
>>> name = "Sarah"
>>> "Hello " + name
'Hello Sarah'
Thonny also has syntax highlighting built in and some support for autocompletion. You can look back on the history of the commands you’ve entered in the REPL with Alt + P
(previous) and Alt + N
(next).
Basic Python usage
Hello world in Python:
print("Hello world")
Simple as that!
Indentation
Some languages use curly braces {
and }
to wrap around lines of code which belong together, and leave it to the writer to indent these lines to appear visually nested. However, Python does not use curly braces but instead requires indentation for nesting. For example a for
loop in Python:
for i in range(10):
print("Hello")
The indentation is necessary here. A second line indented would be a part of the loop, and a second line not indented would be outside of the loop. For example:
for i in range(2):
print("A")
print("B")
would print:
A B A B
whereas the following:
for i in range(2):
print("A")
print("B")
would print:
A A B
Variables
To save a value to a variable, assign it like so:
name = "Bob"
age = 15
Note that data types were not specified with these variables, as types are inferred, and can be changed later.
age = 15
age += 1 # increment age by 1
print(age)
This time I used comments beside the increment command.
Comments
Comments are ignored in the program but there for you to leave notes, and are denoted by the hash #
symbol. Multi-line comments use triple quotes like so:
"""
This is a very simple Python program that prints "Hello".
That's all it does.
"""
print("Hello")
Lists
Python also has lists (called arrays in some languages) which are collections of data of any type:
numbers = [1, 2, 3]
Lists are denoted by the use of square brackets []
and each item is separated by a comma.
Iteration
Some data types are iterable, which means you can loop over the values they contain. For example a list:
numbers = [1, 2, 3]
for number in numbers:
print(number)
This takes each item in the list numbers
and prints out the item:
1 2 3
Note I used the word number
to denote each item. This is merely the word I chose for this - it’s recommended you choose descriptive words for variables - using plurals for lists, and singular for each item makes sense. It makes it easier to understand when reading.
Other data types are iterable, for example the string:
dog_name = "BINGO"
for char in dog_name:
print(char)
This loops over each character and prints them out:
B I N G O
Range
The integer data type is not iterable and trying to iterate over it will produce an error. For example:
for i in 3:
print(i)
will produce:
TypeError: 'int' object is not iterable

However you can make an iterable object using the range
function:
for i in range(3):
print(i)
range(5)
contains the numbers 0
, 1
, 2
, 3
and 4
(five numbers in total). To get the numbers 1
to 5
(inclusive) use range(1, 6)
.
Python files in Thonny
To create a Python file in Thonny, click File > New
and you’ll be given a
For example, in the new window, type:
n = 0
for i in range(1, 101):
n += i
print("The sum of the numbers 1 to 100 is:")
print(n)
Then save this file (File > Save
or Ctrl + S
) and run (Run > Run Module
or hit F5
) and you’ll see the output in your original Python window.
Using the Command Line
You can write a Python file in a standard editor, and run it as a Python script from the command line. Just navigate to the directory the file is saved in (use cd
and ls
for guidance) and run with python3
, e.g. python3 hello.py
.

Other Ways of Using Python
The standard built-in Python shell is accessed by typing python3
in the terminal.
This shell is a prompt ready for Python commands to be entered. You can use this in the same way as Thonny, but it does not have syntax highlighting or autocompletion. You can look back on the history of the commands you’ve entered in the REPL by using the Up/Down keys. Use Ctrl + D
to exit.
IPython
IPython is an interactive Python shell with syntax highlighting, autocompletion, pretty printing, built-in documentation, and more. IPython is not installed by default. Install with:
sudo pip3 install ipython
Then run with ipython
from the command line. It works like the standard python3
, but has more features. Try typing len?
and hitting Enter
. You’re shown information including the docstring for the len
function:
Type: builtin_function_or_method
String Form:<built-in function len>
Namespace: Python builtin
Docstring:
len(object) -> integer
Return the number of items of a sequence or mapping.
Try the following dictionary comprehension:
{i: i ** 3 for i in range(12)}
This will pretty print the following:
{0: 0,
1: 1,
2: 8,
3: 27,
4: 64,
5: 125,
6: 216,
7: 343,
8: 512,
9: 729,
10: 1000,
11: 1331}
In the standard Python shell, this would have printed on one line:
{0: 0, 1: 1, 2: 8, 3: 27, 4: 64, 5: 125, 6: 216, 7: 343, 8: 512, 9: 729, 10: 1000, 11: 1331}

You can look back on the history of the commands you’ve entered in the REPL by using the Up/Down keys like in python
. The history also persists to the next session, so you can exit ipython
and return (or switch between v2/3) and the history remains. Use Ctrl + D
to exit.
Installing Python Libraries
apt
Some Python packages can be found in the Raspberry Pi OS archives, and can be installed using apt, for example:
sudo apt update
sudo apt install python-picamera
This is a preferable method of installing, as it means that the modules you install can be kept up to date easily with the usual sudo apt update
and sudo apt full-upgrade
commands.
pip
Not all Python packages are available in the Raspberry Pi OS archives, and those that are can sometimes be out of date. If you can’t find a suitable version in the Raspberry Pi OS archives, you can install packages from the Python Package Index (known as PyPI).
To do so, install pip:
sudo apt install python3-pip
Then install Python packages (e.g. simplejson
) with pip3
:
sudo pip3 install simplejson
piwheels
The official Python Package Index (PyPI) hosts files uploaded by package maintainers. Some packages require compilation (compiling C/C++ or similar code) in order to install them, which can be a time-consuming task, particlarly on the single-core Raspberry Pi 1 or Raspberry Pi Zero.
piwheels is a service providing pre-compiled packages (called Python wheels) ready for use on the Raspberry Pi. Raspberry Pi OS is pre-configured to use piwheels for pip. Read more about the piwheels project at www.piwheels.org.
GPIO and the 40-pin Header
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A powerful feature of the Raspberry Pi is the row of GPIO (general-purpose input/output) pins along the top edge of the board. A 40-pin GPIO header is found on all current Raspberry Pi boards (unpopulated on Raspberry Pi Zero, Raspberry Pi Zero W and Raspberry Pi Zero 2 W). Prior to the Raspberry Pi 1 Model B+ (2014), boards comprised a shorter 26-pin header. The GPIO header on all boards (including the Raspberry Pi 400) have a 0.1" (2.54mm) pin pitch.

Any of the GPIO pins can be designated (in software) as an input or output pin and used for a wide range of purposes.

Note
|
The numbering of the GPIO pins is not in numerical order; GPIO pins 0 and 1 are present on the board (physical pins 27 and 28) but are reserved for advanced use (see below). |
Voltages
Two 5V pins and two 3.3V pins are present on the board, as well as a number of ground pins (0V), which are unconfigurable. The remaining pins are all general purpose 3.3V pins, meaning outputs are set to 3.3V and inputs are 3.3V-tolerant.
Inputs
A GPIO pin designated as an input pin can be read as high (3.3V) or low (0V). This is made easier with the use of internal pull-up or pull-down resistors. Pins GPIO2 and GPIO3 have fixed pull-up resistors, but for other pins this can be configured in software.
More
As well as simple input and output devices, the GPIO pins can be used with a variety of alternative functions, some are available on all pins, others on specific pins.
-
PWM (pulse-width modulation)
-
Software PWM available on all pins
-
Hardware PWM available on GPIO12, GPIO13, GPIO18, GPIO19
-
-
SPI
-
SPI0: MOSI (GPIO10); MISO (GPIO9); SCLK (GPIO11); CE0 (GPIO8), CE1 (GPIO7)
-
SPI1: MOSI (GPIO20); MISO (GPIO19); SCLK (GPIO21); CE0 (GPIO18); CE1 (GPIO17); CE2 (GPIO16)
-
-
I2C
-
Data: (GPIO2); Clock (GPIO3)
-
EEPROM Data: (GPIO0); EEPROM Clock (GPIO1)
-
-
Serial
-
TX (GPIO14); RX (GPIO15)
-
GPIO pinout
A handy reference can be accessed on the Raspberry Pi by opening a terminal window and running the command pinout
. This tool is provided by the GPIO Zero Python library, which is installed by default in Raspberry Pi OS.

For more details on the advanced capabilities of the GPIO pins see gadgetoid’s interactive pinout diagram.
Warning
|
While connecting up simple components to the GPIO pins is perfectly safe, it’s important to be careful how you wire things up. LEDs should have resistors to limit the current passing through them. Do not use 5V for 3.3V components. Do not connect motors directly to the GPIO pins, instead use an H-bridge circuit or a motor controller board. |
Permissions
In order to use the GPIO ports your user must be a member of the gpio
group. The pi
user is a member by default, other users need to be added manually.
sudo usermod -a -G gpio <username>
GPIO in Python
Using the GPIO Zero library makes it easy to get started with controlling GPIO devices with Python. The library is comprehensively documented at gpiozero.readthedocs.io.
LED
To control an LED connected to GPIO17, you can use this code:
from gpiozero import LED
from time import sleep
led = LED(17)
while True:
led.on()
sleep(1)
led.off()
sleep(1)
Run this in an IDE like Thonny, and the LED will blink on and off repeatedly.
LED methods include on()
, off()
, toggle()
, and blink()
.
Button
To read the state of a button connected to GPIO2, you can use this code:
from gpiozero import Button
from time import sleep
button = Button(2)
while True:
if button.is_pressed:
print("Pressed")
else:
print("Released")
sleep(1)
Button functionality includes the properties is_pressed
and is_held
; callbacks when_pressed
, when_released
, and when_held
; and methods wait_for_press()
and wait_for_release
.
Button + LED
To connect the LED and button together, you can use this code:
from gpiozero import LED, Button
led = LED(17)
button = Button(2)
while True:
if button.is_pressed:
led.on()
else:
led.off()
Alternatively:
from gpiozero import LED, Button
led = LED(17)
button = Button(2)
while True:
button.wait_for_press()
led.on()
button.wait_for_release()
led.off()
or:
from gpiozero import LED, Button
led = LED(17)
button = Button(2)
button.when_pressed = led.on
button.when_released = led.off
Going further
You can find more information on how to program electronics connected to your Raspberry Pi with the GPIO Zero Python library in the Raspberry Pi Press book Simple Electronics with GPIO Zero. Written by Phil King, it is part of the MagPi Essentials series published by Raspberry Pi Press. The book gets you started with the GPIO Zero library, and walks you through how to use it by building a series of projects.
You can download this book as a PDF file for free, it has been released under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY NC-SA) licence.