Python – What I Broke – Programming and Web Development

A4988 Stepper motor RaspberryPi

We’re using a 42shd0034-20B Geetech stepping motor taken from a 3d printer:

We’ll be driving it with an A4988 stepper motor controller. You can pick up five packs of these for less than $2 online – definitely worth having a few extras around:

The datasheet is available here: https://www.pololu.com/file/download/A4988.pdf?file_id=0J450

The following diagram illustrates what we’ll be doing:

Once everything is connected it’ll end up looking something like this:

To start, connect your stepping and direction pins. I’ve used GPIO16 for stepping and GPIO21 for direction:

Each time GPIO16 is set to HIGH it will make the stepper motor take one step. When the direction pin is HIGH the stepper motor will go clockwise, when it’s LOW, anti-clockwise.

If you’re not using the sleep functionality, connect the RESET and SLP pins together and then wire them directly to 3.3v:

Using a separate power source wire 12v to the GND and VMOT pins. You should also place a capacitor across these pins as close to the board as possible. Generally the longest leg is positive. You’ll also need to connect the external GND to the Raspberry Pi’s GND:

Connect the four pins of the stepper motor:

Connect the A4988 to 3.3v and common GND:

The code is pretty straight forward but I’ve provided a class below to help you get started:

# System imports import RPi.GPIO as GPIO from time import sleep


class StepperHandler():
   __CLOCKWISE = 1

   __ANTI_CLOCKWISE = 0
   def __init__(self, stepPin, directionPin, delay=0.208, stepsPerRevolution=200):
      # Configure instance

      self.CLOCKWISE = self.__CLOCKWISE

      self.ANTI_CLOCKWISE = self.__ANTI_CLOCKWISE

      self.StepPin = stepPin

      self.DirectionPin = directionPin

      self.Delay = delay

      self.RevolutionSteps = stepsPerRevolution

      self.CurrentDirection = self.CLOCKWISE

      self.CurrentStep = 0
      # Setup gpio pins

      GPIO.setmode(GPIO.BCM)

      GPIO.setwarnings(False)

      GPIO.setup(self.StepPin, GPIO.OUT)

      GPIO.setup(self.DirectionPin, GPIO.OUT)
   def Step(self, stepsToTake, direction = __CLOCKWISE):
      print("Step Pin: " + str(self.StepPin) + " Direction Pin: " + str(self.DirectionPin) + " Delay: " + str(self.Delay))

      print("Taking " + str(stepsToTake) + " steps.")
      # Set the direction

      GPIO.output(self.DirectionPin, direction)
      # Take requested number of steps

      for x in range(stepsToTake):

         print("Step " + str(x))

         GPIO.output(self.StepPin, GPIO.HIGH)

         self.CurrentStep += 1

         sleep(self.Delay)

         GPIO.output(self.StepPin, GPIO.LOW)

         sleep(self.Delay)
# Define pins

STEP_PIN = 16

DIRECTION_PIN = 21
# Create a new instance of our stepper class (note if you're just starting out with this you're probably better off using a delay of ~0.1)

stepperHandler = StepperHandler(STEP_PIN, DIRECTION_PIN, 0.0025)
# Go forwards once

stepperHandler.Step(200)
# Go backwards once

stepperHandler.Step(200, stepperHandler.ANTI_CLOCKWISE)

4: /codebuild/output/tmp/script.sh: pip: not found – Node.js and CodeStar

Hi everyone,

I ran into the following CodeBuild error after upgrading my build environment from the default nodejs8.10 to nodejs10.14:

4: /codebuild/output/tmp/script.sh: pip: not found

This one was a little confusing, but thankfully fairly easy to fix. In your buildspec.yml file update the pip steps to reference pip3 instead of pip:

// Original
commands:
      # Install dependencies needed for running tests
      - npm install

      # Upgrade AWS CLI to the latest version
      - pip install --upgrade awscli

// Modified
commands:
      # Install dependencies needed for running tests
      - npm install

      # Upgrade AWS CLI to the latest version
      - pip3 install --upgrade awscli

AWS IoT – error in discovery certificate_verify_failed

Hi everyone,

I ran into the following error while using the AWS IoT python SDK:

Error in discovery!
Type: 
Error message: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:720)

It turns out that this was because I was using the wrong root certificate. In the documentation there are five certificates listed:

RSA 2048 bit key: VeriSign Class 3 Public Primary G5 root CA certificate
RSA 2048 bit key: Amazon Root CA 1
RSA 4096 bit key: Amazon Root CA 2
ECC 256 bit key: Amazon Root CA 3
ECC 384 bit key: Amazon Root CA 4

If you’re using the console to create the certificate and have already downloaded your device cert, public cert and private key you can use Amazon Root CA 1: https://www.amazontrust.com/repository/AmazonRootCA1.pem

As soon as that was added the error was resolved and I was able to move onto the next one. I found most of the info on the AWS forums but let me know if you have any questions: https://forums.aws.amazon.com/thread.jspa?threadID=286871

AttributeError: module ‘serial’ has no attribute ‘SerialException’ – Python 3.5

Hi everyone,

A quick fix for an error I ran into while updating to Pyhton 3.5.2:

AttributeError: module 'serial' has no attribute 'SerialException'

I needed to add pyserial:

pi@raspberrypi:~/Desktop/piscripts/get-commands $ sudo pip3.5 install pyserial
Collecting pyserial
  Downloading pyserial-3.4-py2.py3-none-any.whl (193kB)
    100% |████████████████████████████████| 194kB 530kB/s
Installing collected packages: pyserial
Successfully installed pyserial-3.4

Thanks to the following link: https://stackoverflow.com/a/47562659/522859

Could not find a version that satisfied the requirement smbus/python3-smbus

Hi everyone,

I ran into a bit of an issue installing smbus on Python3.5. It looks like all you have to do is use smbus2:

pip3.5 install smbus2

Collecting smbus2
Downloading smbus2-0.2.0.tar.gz
Building wheels for collected packages: smbus2
Running setup.py bdist_wheel for smbus2 … done
Stored in directory: /root/.cache/pip/wheels/90/71/b4/9f90d8e2d0349ab55fef07169a81bd8f925965f16174e2f809
Successfully built smbus2
Installing collected packages: smbus2
Successfully installed smbus2-0.2.0

Thanks to the following link: https://www.raspberrypi.org/forums/viewtopic.php?t=192909

Pillow Install Fails – Python 3.5.2

Hi everyone,

I ran into a bit of an issue trying to install Pillow on Raspbian with Python 3.5.2. The full error is below, but the solution was simply to install the following:

sudo apt-get install libjpeg8-dev sudo pip3.5 install pillow

sudo pip3.5 install pillow
Collecting pillow
Using cached Pillow-4.3.0.tar.gz
Requirement already satisfied: olefile in /usr/local/lib/python3.5/site-packages (from pillow)
Installing collected packages: pillow
Running setup.py install for pillow … error
Complete output from command /usr/local/bin/python3.5 -u -c “import setuptools, tokenize;__file__=’/tmp/pip-build-inj0l_9q/pillow/setup.py’;f=getattr(tokenize, ‘open’, open)(__file__);code=f.read().replace(‘rn’, ‘n’);f.close();exec(compile(code, __file__, ‘exec’))” install –record /tmp/pip-xp_x4w_5-record/install-record.txt –single-version-externally-managed –compile:
running install
running build
running build_py
creating build
creating build/lib.linux-armv7l-3.5
creating build/lib.linux-armv7l-3.5/PIL
copying PIL/MicImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageMath.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/WebPImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImagePath.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageGrab.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/SunImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/__init__.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageEnhance.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageMorph.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/XpmImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/EpsImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/FtexImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/WmfImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/FitsStubImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageDraw2.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/IptcImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/_binary.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/MpoImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/Hdf5StubImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/Image.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/MspImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageWin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GimpPaletteFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageTk.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PSDraw.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/McIdasImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/SgiImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageStat.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageChops.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PdfImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/features.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PcfFontFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PcxImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageOps.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImagePalette.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/TgaImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageSequence.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/_util.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/TiffTags.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/BmpImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/DdsImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ExifTags.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PyAccess.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PpmImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageCms.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PaletteFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/XVThumbImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/IcoImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageFilter.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageFont.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GifImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GbrImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/XbmImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PngImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/FontFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/IcnsImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/TiffImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/_tkinter_finder.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/DcxImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/OleFileIO.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/SpiderImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/JpegImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GribStubImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/MpegImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PalmImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/BdfFontFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GimpGradientFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PsdImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/WalImageFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PcdImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/version.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/FpxImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageQt.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/Jpeg2KImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageDraw.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/GdImageFile.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ContainerIO.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/CurImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/FliImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageMode.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/JpegPresets.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/PixarImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageColor.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/BufrStubImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageTransform.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImageShow.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/TarIO.py -> build/lib.linux-armv7l-3.5/PIL
copying PIL/ImtImagePlugin.py -> build/lib.linux-armv7l-3.5/PIL
running egg_info
writing dependency_links to Pillow.egg-info/dependency_links.txt
writing requirements to Pillow.egg-info/requires.txt
writing top-level names to Pillow.egg-info/top_level.txt
writing Pillow.egg-info/PKG-INFO
warning: manifest_maker: standard file ‘-c’ not found

reading manifest file ‘Pillow.egg-info/SOURCES.txt’
reading manifest template ‘MANIFEST.in’
warning: no files found matching ‘*.sh’
no previously-included directories found matching ‘docs/_static’
warning: no previously-included files found matching ‘.coveragerc’
warning: no previously-included files found matching ‘codecov.yml’
warning: no previously-included files found matching ‘.editorconfig’
warning: no previously-included files found matching ‘.landscape.yaml’
warning: no previously-included files found matching ‘.travis’
warning: no previously-included files found matching ‘.travis/*’
warning: no previously-included files found matching ‘appveyor.yml’
warning: no previously-included files found matching ‘build_children.sh’
warning: no previously-included files found matching ‘tox.ini’
warning: no previously-included files matching ‘.git*’ found anywhere in distribution
warning: no previously-included files matching ‘*.pyc’ found anywhere in distribution
warning: no previously-included files matching ‘*.so’ found anywhere in distribution
writing manifest file ‘Pillow.egg-info/SOURCES.txt’
running build_ext

The headers or library files could not be found for jpeg,
a required dependency when compiling Pillow from source.

Please see the install instructions at:
https://pillow.readthedocs.io/en/latest/installation.html

Traceback (most recent call last):
File “/tmp/pip-build-inj0l_9q/pillow/setup.py”, line 787, in
zip_safe=not (debug_build() or PLATFORM_MINGW), )
File “/usr/local/lib/python3.5/distutils/core.py”, line 148, in setup
dist.run_commands()
File “/usr/local/lib/python3.5/distutils/dist.py”, line 955, in run_commands
self.run_command(cmd)
File “/usr/local/lib/python3.5/distutils/dist.py”, line 974, in run_command
cmd_obj.run()
File “/usr/local/lib/python3.5/site-packages/setuptools/command/install.py”, line 61, in run
return orig.install.run(self)
File “/usr/local/lib/python3.5/distutils/command/install.py”, line 539, in run
self.run_command(‘build’)
File “/usr/local/lib/python3.5/distutils/cmd.py”, line 313, in run_command
self.distribution.run_command(command)
File “/usr/local/lib/python3.5/distutils/dist.py”, line 974, in run_command
cmd_obj.run()
File “/usr/local/lib/python3.5/distutils/command/build.py”, line 135, in run
self.run_command(cmd_name)
File “/usr/local/lib/python3.5/distutils/cmd.py”, line 313, in run_command
self.distribution.run_command(command)
File “/usr/local/lib/python3.5/distutils/dist.py”, line 974, in run_command
cmd_obj.run()
File “/usr/local/lib/python3.5/distutils/command/build_ext.py”, line 338, in run
self.build_extensions()
File “/tmp/pip-build-inj0l_9q/pillow/setup.py”, line 577, in build_extensions
raise RequiredDependencyException(f)
__main__.RequiredDependencyException: jpeg

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File “”, line 1, in
File “/tmp/pip-build-inj0l_9q/pillow/setup.py”, line 799, in
raise RequiredDependencyException(msg)
__main__.RequiredDependencyException:

The headers or library files could not be found for jpeg,
a required dependency when compiling Pillow from source.

Please see the install instructions at:
https://pillow.readthedocs.io/en/latest/installation.html

—————————————-
Command “/usr/local/bin/python3.5 -u -c “import setuptools, tokenize;__file__=’/tmp/pip-build-inj0l_9q/pillow/setup.py’;f=getattr(tokenize, ‘open’, open)(__file__);code=f.read().replace(‘rn’, ‘n’);f.close();exec(compile(code, __file__, ‘exec’))” install –record /tmp/pip-xp_x4w_5-record/install-record.txt –single-version-externally-managed –compile” failed with error code 1 in /tmp/pip-build-inj0l_9q/pillow/

Thanks to the comment on the following Stackoverflow post for the solution: https://stackoverflow.com/a/34631976/522859

Updating to Python 3.5.1 on RaspberryPi

Hi everyone,

Just a quick post on how to update to Python 3.5.1 the normal upgrade process isn’t working for you:

cd ~ wget https://www.python.org/ftp/python/3.5.1/Python-3.5.1.tgz tar -zxvf Python-3.5.1.tgz cd Python-3.5.1 ./configure && make && sudo make install

You may need to restart once this is complete. Run the following to confirm that the version is 3.5.1:
pi@raspberrypi:~ $ python3 --version Python 3.5.1

Check out the following link for more info: https://stackoverflow.com/a/37079319/522859

Check Tensorflow Version – Raspbian

Hey everyone,

Just a quick post on how to check the Tensorflow version on Raspbian with a one-liner (assumes Python 3.x):

python3 -c 'import tensorflow as tf; print(tf.__version__)'

Check out this Stackoverflow post for more info: https://stackoverflow.com/a/38549357/522859

AttributeError: ‘dict’ object has no attribute ‘iteritems’ – Python

Hey everyone,

Just running through object detection samples for Tensorflow and I encountered the following error:

Sample: https://github.com/GoogleCloudPlatform/tensorflow-object-detection-example

AttributeError: ‘dict’ object has no attribute ‘iteritems’

The issue seems to be that the sample hasn’t been made compatible with Python 3.x. Simply make the following change and it should work:

# Original for cls, new_image in new_images.iteritems():

# Changed for cls, new_image in new_images.items():

Thanks to the following StackOverflow post: https://stackoverflow.com/a/30418498/522859

Converting proto files to .py on Windows – Tensorflow

Hey everyone,

Ran into a bit of an issue today with Tensorflow:

ImportError: cannot import name preprocessor_pb2

Turned out that I hadn’t run some of the installing steps. I needed to use protoc to convert the proto directory files:
protoc object_detection/protos/preprocessor_pb2.proto --python_out=.

This turned out to be a bit of a headache as well, but thankfully a github post explained it all pretty well:

Here are the steps I followed to install it for windows:
(Prerequisite, you must have python, pip and)

Choose a Python release from here and download: Link here
– Extract the tar.gzor zip
– Open a cmd and pip install the following: pillow, lxml, jupyter, matplotlib
– Copy the protoc.exe from the protoc folder (you don’t need to do all the CMake steps you might have stumbled upon, it worked for me without them too) and paste it into your protos folder in the object detection directory.
– Run the protoc for each of those protos like “protoc object_detection/protos/*.proto –python_out=.”. . Note that you might encounter a problem with the paths and there’s two ways around that: Either move the protoc.exe two folders down or do the noobish thing that I did – copy the protos and paste them into a new directory inside the protos folder ‘object_detectionprotos’ so you would have a folder structure like’object_detectionprotosobject_detectionprotos’ (If it looks stupid but it works, it’s not stupid eh?) Note that *.proto might also not work and you might have to do each of them individually
– You are done. 🙂 Try to run something to see if you have any problems. You might have to install a manual version of numpyandscipy

GitHub Link: https://github.com/tensorflow/models/issues/1934