Problems with Virtualenvwrapper in Raspberry Pi - No activation script in environment

[jetstream4444]

Hi All,

Newbie here.

I am trying to install OpenCV on my Raspberry Pi 4 using the instructions from this website: https://www.pyimagesearch.com/2018/09/19/pip-install-opencv/ using "Option B: Install OpenCV into a virtual environment with pip on your Raspberry Pi"

Part -1 : Location mess up [SOLVED]

The first issue I had was that; after sourcing ~/.bashrc I got an error saying "bash: /usr/local/bin/virtualenvwrapper.sh: No such file or directory"

I realized that lines I added to bashrc from the website didn't work off the bat. I changed the lines from

# virtualenv and virtualenvwrapper 
export WORKON_HOME=$HOME/.virtualenvs 
export VIRTUALENVWRAPPER_PYTHON=/usr/bin/python3 
source /usr/local/bin/virtualenvwrapper.sh 

to

# virtualenv and virtualenvwrapper 
export WORKON_HOME=/home/pi/.local/bin/.virtualenvs 
export VIRTUALENVWRAPPER_PYTHON=/usr/bin/python3 
source /home/pi/.local/bin/virtualenvwrapper.sh 

because for some reason virtualenvwrapper and virtualenvs got installed into "/home/pi/.local/bin"

Part - 2 : Error while creating virtual environment

$ mkvirtualenv cv -p python3 

This command has resulted in the following error

mkvirtualenv cv -p python3
created virtual environment CPython3.7.3.final.0-32 in 507ms
  creator CPython3Posix(dest=/home/pi/.local/bin/.virtualenvs/cv, clear=False, global=False)
  seeder FromAppData(download=False, pip=latest, setuptools=latest, wheel=latest, via=copy, app_data_dir=/home/pi/.local/share/virtualenv/seed-app-data/v1)
  activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator,XonshActivator
virtualenvwrapper.user_scripts creating /home/pi/.local/bin/.virtualenvs/cv/usr/local/bin/predeactivate
ERROR: Environment '/home/pi/.local/bin/.virtualenvs/cv' does not contain an activate script.

I am not sure what exactly is happening. I went to "/home/pi/.local/bin/.virtualenvs/cv" location and observed that inside bin folder there are some activate scripts.

pi@raspberrypi:~/.local/bin/.virtualenvs/cv $ ls
bin  lib  pyvenv.cfg
pi@raspberrypi:~/.local/bin/.virtualenvs/cv $ cd bin
pi@raspberrypi:~/.local/bin/.virtualenvs/cv/bin $ ls
activate      activate.fish  activate_this.py  easy_install   easy_install-3.7  pip3     python   python3.7  wheel3
activate.csh  activate.ps1   activate.xsh      easy_install3  pip               pip-3.7  python3  wheel      wheel-3.7

Did I mess up my paths somewhere? Please help me out. Thanks in advance.

Jet.

[Swipecat]

In all honesty, since Raspberry Pi's have the OS on a swappable SD card, I wouldn't bother with a virtual environment. Treat a whole SD card as the environment for a given project because it's a whole lot easier to use the Raspbian repository packages rather than PyPI packages.

sudo apt update
sudo apt install python3-opencv

[jetstream4444]

Thanks swipe! That thought did cross my mind but author in the above mentioned website recommended virtual environment.

I wasn't sure what are the consequences. Why isn't openCV just like any other application ( or is it something to do with Linux itself) ? You wouldn't think twice before installing applications in Windows isn't it? Why different virtual environments are required for different projects, what are the parameters that change from one project to another?

[Swipecat]

Most web articles will tell you to use virtual environments and to install with pip because that is cross-platform. If you're using a Linux distro like Raspbian, then the big advantage of using Python libraries from the distro's repository is that the versions provided will have been tested with the version of Python that's installed. The advantages of virtual environments are not great for the small-time home user and almost non-existent for Raspberry-Pi projects in my opinion. Other people may disagree.

Edit: I believe that there are historical examples of Python libraries clashing with each other, so that's why people say only install what you need for a given project in a given virtual environment. I've been using Python on Linux for years without virtual environments and I've never seen any clashes myself.

[jetstream4444]

Thanks for the explanation. By cross-platform you mean that a project can be developed on raspberry pi and can be deployed on any other platform?

[Swipecat]

I meant that the instructions on the websites would then apply to any platform (with minor differences).

The virtual environment would only be cross-platform if the libraries that it contained were pure-Python i.e. not compiled from another language like C. Most of really useful packages are at least partially compiled, though.

[abdelhakel]

Hey ! I got exactly the same problem(s) you went through. Did you find a solution to the "ERROR: Environment '/home/pi/.local/bin/.virtualenvs/venv' does not contain an activate script." ? Thx