No guarantee that Dockerfile and piplock will be compatible, leading to error installing psychopg2 about djangoforprofessionals

[wsvincent]

Yes, I think you are correct. I've updated the newer versions of the book to use Python 3.8 but this is a very likely gotcha for newcomers. Thank you for pointing it out. I like your idea of using the requires feature; I think I'll use that in the new text!

[lapulgaatomica]

I ran into an error, which I've fixed, but that could be a trap for new users. It stems from having a system install of python 3.8, and the book (sample at least) relying on python 3.7. Admittedly your prior book does have extensive and useful dev environment set-up instructions, but not this one.

I have python 3.8 installed on my system as the user default. Therefore, the piplock file will default to:

[requires]
python_version = "3.8"

When you get to install the psycopg2 package, the error that is thrown is:

❯ docker-compose exec web pipenv install psycopg2-binary==2.8.3
Warning: Python 3.8 was not found on your system…
Neither 'pyenv' nor 'asdf' could be found to install Python.
You can specify specific versions of Python with:
$ pipenv --python path/to/python

I believe the error arises from how the Dockerfile and the piplock at this point differ, with the Dockerfile specifying 3.7. If the piplock gets changed manually to 3.7 however, then the install runs as expected.

A potential guarantee may be adding the --python 3.7 on pipenv creation.

I'm not sure what you mean by "adding --python 3.7 on pipenv creation" can you please explain?

[DaveParr]

@lapulgaatomica pipenv is a way of managing environments and dependencies for python.

https://pypi.org/project/pipenv/

In this particular case, and from memory now almost a year back @wsvincent in his (great) books, I think introduces people following through the work on their computers in a way that encourages them to use pipenv to set up their projects. In this case I was making a (soft) recommendation that for future copies of the book he includes the instruction to run pipenv --python 3.7 as this will set the project up in a way that, at the time, fixed a dependcy issue with psychopog2.

If you go the website listed above and look at the usage section on the front page it says:

"Usage Examples:
Create a new project using Python 3.7, specifically:
$ pipenv --python 3.7"

this is what I was referring to.

Hope that helps :)