I have yet to come across an answer that makes me WANT to start using virtual environments. I understand how they work, but what I don’t understand is how can someone (like me) have hundreds of Python projects on their drive, almost all of them use the same packages (like Pandas and Numpy), but if they were all in separate venv’s, you’d have to pip install those same packages over and over and over again, wasting so much space for no reason. Not to mention if any of those also require a package like tensorflow.

The only real benefit I can see to using venv’s in my case is to mitigate version issues, but for me, that’s really not as big of an issue as it’s portrayed. Any project of mine that becomes out of date, I update the packages for it.

Why install the same dependency for every project when you can just do it once for all of them on a global scale? I know you can also specify —-global-dependencies or whatever the tag is when creating a new venv, but since ALL of my python packages are installed globally (hundreds of dependencies are pip installed already), I don’t want the new venv to make use of ALL of them? So I can specify only specific global packages to use in a venv? That would make more sense.

What else am I missing?

UPDATE

I’m going to elaborate and clarify my question a bit as there seems to be some confusion.

I’m not so much interested in understanding HOW venv’s work, and I understand the benefits that can come with using them. What I’m asking is:

1. Why would someone with (for example) have 100 different projects that all require tensorflow to be installed into their own venv’s. That would mean you have to install tensorflow 100 separate times. That’s not just a “little” extra space being wasted, that’s a lot.

2. I understand they mitigate dependency versioning issues, you can “freeze” packages with their current working versions and can forget about them, great. And maybe I’m just unique in this respect, but the versioning issue (besides the obvious difference between python 2 and 3) really hasn’t been THAT big of an issue. Yes I’ve run into it, but isn’t it better practise to keep your projects up to date with the current working/stable versions than to freeze them with old, possibly no longer supported versions? Sure it works, but that doesn’t seem to be the “best” option to me either.

To reiterate on the second part of my question, what I would think is, if I have (for example) tensorflow installed globally, and I create a venv for each of my 100 tensorflow projects, is there not a way to make use of the already globally installed tensorflow inside of the venv, without having to install it again? I know in pycharm and possibly the command line, you can use a — system-site-packages argument (or whatever it is) to make that happen, but I don’t want to include ALL of the globally installed dependencies, cuz I have hundreds of those too. Is —-system-site-packages -tensorflow for example a thing?

Hope that helps to clarify what I’m looking for out of this discussion because so far, I have no use for venv’s, other than from everyone else claiming how great they are but I guess I see it a bit differently :P

(FINAL?) UPDATE

From the great discussions I've had with the contributors below, here is a summation of where I think venv's are of benefit and where they're not:

USE a venv:

1. You're working on one BIG project with multiple people to mitigate versioning issues among the people
2. You don't plan on updating your dependencies very often for all projects
3. To have a clearer separation of your projects
4. To containerize your project (again, for distribution)
5. Your portfolio is fairly small (especially in the data science world where packages like Tensorflow are large and used quite frequently across all of them as you'd have to pip install the same package to each venv)

DO NOT use a venv:

1. Your portfolio of projects is large AND requires a lot of heavy dependencies (like tensorflow) to mitigate installing the same package in every venv you create
2. You're not distributing your projects across a team of people
3. You're actively maintaining your projects and keeping global dependency versions up to date across all of them (maybe I'm the only one who's actually doing this, but whatever)

As was recently mentioned, I guess it depends on your use case. Working on a website that requires contribution from many people at once, it makes sense to all be working out of one environment, but for someone like me with a massive portfolio of Tensorflow projects, that do not have versioning issues or the need for other team members, it doesn't make sense. Maybe if you plan on containerizing or distributing the project it makes sense to do so on an individual basis, but to have (going back to this example) 100 Tensorflow projects in your portfolio, it makes no sense to have 100 different venv's for all of them as you'd have to install tensorflow 100 times into each of them, which is no different than having to pip install tensorflow==2.2.0 for specific old projects that you want to run, which in that case, just keep your projects up to date.

Maybe I'm missing something else major here, but that's the best I've come up with so far. Hope it helps someone else who's had a similar thought.

CodePudding user response：

I'm a data scientist and sometimes I run into these things called "virtual environments" and I don't get what the use case is? I already have all of these packages and modules and widgets downloaded! Why should I set up a separate place where I manage all of the stuff I'm already managing globally?

Python is a very powerful tool that can do a lot of things. In this answer consider two such ways to swing the metaphorical hammer:

• Data Science
• Software Engineering

For a data scientist (working alone) using Python to write a poc for a research paper, make a lstm nn, or predict the price of TSLA dependent on the frequency of Elon Musk's tweets all that really matters is being able to use the best library (tensorflow, pytorch, sklearn, ...) for whatever task they're trying to get done. In whatever directory they're working in when they need it. It is very tempting to use one global Python installation and just use the same stuff everywhere. Frankly, this is probably fine. As it's just one person managing their own space. So the configuration of their machine would be one single Python environment and everything, everywhere uses it. Or if the data scientist wanted to they could have a single directory that contains a virtual environment and some sub directories containing all the scripts (projects) they work on.

Now consider a software engineer who has multiple git repos with complete CI/CD pipelines that each build into separate entities that then get deployed to some cloud environment. Them and the 9 other people on their team need to be able to be sure that they are all making changes that won't break any piece of the code. For example in Python 3.6 the function dict.popitem subtly changed from returning a random element in a dict to LIFO order guaranteed. It's pretty easy to see that that could cause issues if Jerry had implemented a function that relies on the original random nature of the function and Bob implemented a function with the LIFO behavior guaranteed. This team of engineers would have git repos that each contain a single virtual environment (a single isolated Python environment) that allows them to manage dependencies for that "project".

So the data scientist has one Python installation/environment that allows them to do whatever.

The engineer has a Python installation and a bunch of environments so that they can work across multiple repos with multiple people and (hopefully) nothing breaks.

CodePudding user response：

I can see where you're coming from with your question. It can seem like a lot of work to set up and maintain multiple virtual environments (venvs), especially when many of your projects might use similar or even the same packages.

However, there are some good reasons for using venvs even in cases where you might be tempted to just use a single global environment. One reason is that it can be helpful to have a clear separation between your different projects. This can be helpful in terms of organization, but it can also be helpful if you need to use different versions of packages in different projects.

If you try to share a single venv among all of your projects, it can be difficult to use different versions of packages in those projects when necessary. This is because the packages in your venv will be shared among all of the projects that use that venv. So, if you need to use a different version of a package in one project, you would need to change the version in the venv, which would then affect all of the other projects that use that venv. This can be confusing and make it difficult to keep track of what versions of packages are being used in which projects.

Another issue with sharing a single venv among all of your projects is that it can be difficult to share your code with others. This is because they would need to have access to the same environment (which contains lots of stuff unrelated to the single project you are trying to share). This can be confusing and inconvenient for them.

So, while it might seem like a lot of work to set up and maintain multiple virtual environments, there are some good reasons for doing so. In most cases, it is worth the effort in order to have a clear separation between your different projects and to avoid confusion when sharing your code with others.

CodePudding user response：

It's the same principle as in monouser vs multiuser, virtualization vs no virtualization, containers vs no containers, monolithic apps vs micro services, etcetera; to avoid conflict, maintain order, easily identify a state of failure, among other reasons as scalability or portability. If necessary apply it, and always keeping in mind KISS philosophy as well, managing complexity, not creating more.

And as you have already mentioned, considering that resources are finite.

Besides, a set of projects that share the same base of dependencies of course that is not the best example of separation necessity. In addition to that, technology evolve taking into account not redundancy of knowingly base of commonly used resources.

CodePudding user response：

Well, there are a few advantages:

• with virtual environments, you have knowledge about your project's dependencies: without virtual environments your actual environment is going to be a yarnball of old and new libraries, dependencies and so on, such that if you want to deploy a thing into somewhere else (which may mean just running it in your new computer you just bought) you can reproduce the environment it was working in
• you're eventually going to run into something like the following issue: project alpha needs version7 of library A, but project beta needs library B, which runs on version3 of library A. if you install version3, A will probably die, but you really need to get B working.
• it's really not that complicated, and will save you a lot of grief in the long term.

CodePudding user response：

There are several motivations for venvs, or for their moral equivalent: conda environments.

1. author a package

You create a cool "scrape my favorite site" package which graphs a timeseries of some widget product. Naturally it depends on BeautifulSoup. You happened to have html5lib 1.1 lying around due to some previous project, so you tested with that. A user downloads your scrape-widget package from pypi, happens to have lxml 4.7.1 available, and finds that scraping crashes when using that library. Wouldn't it have been better for your package to specify that user shall run against the same deps that you tested with?

2. use a package

Same scenario, but now you're using someone's scrape-widget package. Author tested with lxml 4.7.1 but you have lxml 4.9.1, which behaves differently, and this makes the app behave differently, crashing in ways the author never saw.

3. use two packages

You want to run both scrape-frobozz-magic-widgets and scrape-acme-widget. Their authors tested using different versions of requests, and of lxml. Changing dep changes the app behavior. You can only use one or the other, unless you're willing to re-run pip quite frequently.

4. collaborate on a team

You write code that has deps. So does your colleague. You have to coordinate things, so testing on one laptop instills confidence the test would succeed on other laptops.

5. use CI

You have a teammate named Jenkins, and want to communicate to him that you used a specific version of a dep when you saw the test succeed.

6. get a new laptop

Things were working. Then your laptop exploded, you got a new one, and you (quickly) want to see things work again. Some of your deps were downrev, due to recently released bugs and breaking changes. Reading a file full of dep versions from your github repo lets you immediately reproduce the state of the world back when things were working.