When learning to develop Django and Flask Python applications using virtual environment I did not know that I should activate the virtual environment before running the application. Well, more precisely, I did know the virtual env should be activated but rather I assumed it would be activated somehow auto-magically.
I was using MS Visual Studio 2015 RC and its new Python Tools which work fine by the way. One can install new Python/Flask/Django/etc modules via the IDE.
This was also the first time I was using Python virtual environment. I hadn’t previously done any Python web development. I had used Python for analytical purposes in files, command line and iPython but all of these used the ‘native’ operating system Python installation.
In MS VS 2015 RC, after Python Tools are installed, there are templates to create new Django or Flask projects, and one of the steps asks if I want to install virtual env or not.
So after a bit of search and read I realized virtual env is the way to go. Its better for many reasons to have a standalone Python environment for each new Python/Flask/Django project.
I just assumed that since I had created my new Python application with a virtual env that when I opened Visual Studio and started working on it, it would be in virtual environment by default somehow auto-magically.
But no, the virtual environment has to be activated manually each time the project is opened or before being able to interact with the project via web browser. So remember to activate your virtual env before running your Python/Flash/Django application.
What mislead me was that running the application without first activating the virtual environment can often be ok because the native operating system Python installation has the required modules, so application runs just fine.
But I ran into problems when after installing new Python modules only to see the application complaining that they weren’t available eg got error message in browser and command line from the server saying ‘no module named xxx’. This was confusing because I was thinking hey I just installed that.
So remember activating the virtual env before running the Python application is required. Now it is second nature to do this.
To activate the virtual env in Windows simply navigate to the ‘Scripts’ folder in your virtual env folder and run the ‘activate.bat’ file.
In command line enter ‘activate’ in that folder. Or you can enter the full path to the activate.bat from anywhere in command line.
You can easily see if virtual env has been started because when it is you will see ‘(env)’ at the start of the command line.
Then you can go back to your application folder with the ‘runserver.py’ (or whatever you call it) and then start the application!