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Python has a lot of different versions.

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Python 2 isn't really supported at all anymore, so we're

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not even going to go over Python 2,

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but Python 3.5, for example, is still very popular, and it

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doesn't support things like an f-string.

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So let's just go into our IPython here and we could do 'name

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= "Kalob", and as an f-string, we could say "Hello

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". And it says, "Hello Kalob".

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And it just happens to be that Python 3.5 does not support

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that. So what if you're using a specific version of Python

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on a specific project?

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Let's say you just get hired at a new company and you run

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'python -V', and you're using Python 3.7,

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but they're using Python 3.8, and they're using a feature

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that's only available in Python 3.8 called the 'walrus

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operator'. Well, you can no longer use Python 3.7.

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You need to upgrade, but you don't necessarily always want

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to just upgrade to 3.8.

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You might also want to keep 3.7 around because you have other

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projects that still use Python 3.7.

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Now, for the most part, that's actually not really gonna

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be a problem, just because Python is for the most part quite

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reverse compatible.

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Meaning if you have Python 3.8 installed and your projects

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are using Python 3.7, chances are your projects using 3.7

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will probably work still.

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But there is the occasional time where that is not true.

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So given this hypothetical situation where you just get hired

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at a new company and you need to use a different version

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of Python, how do you get it?

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Well, there's a thing called 'pyenv', and if we open up our browser,

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and I think it's just 'github.com/pyenv/pyenv', I hope that's correct.

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Yep, looks like it. 'pyenv' is basically 'py environment', and that

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allows you to have different versions of Python.

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And let's read the description.

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'pyenv lets you easily switch between multiple versions of

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Python. It's simple, unobtrusive, and follows the Unix tradition

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of single-purpose tools that do one thing

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well'. I would say that's true.

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I use it quite a bit,

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I really like it. Table of contents,

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let's go down to 'Installation'.

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So if you are on a Mac, you can consider installing it with

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Homebrew, and let's click on that.

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And it is simple as 'brew.

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update, brew install pyenv'.

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If you're on a Mac, and you don't have 'brew', you might want

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to get 'Homebrew'. It is a nice little package manager.

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It's like 'pip', but for your macOS. If you're on Windows

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you're gonna have to use 'pyenv-win' because Windows is a little bit different.

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It's not really Unix based at all, whereas Mac actually has

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a little bit of Unix inner workings inside of it still.

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So if you're on Windows, definitely check out 'github.com/

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pyenv-win/pyenv-win'.

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And so if you want, you can go ahead and get that installed.

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Now before you do that,

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if you have Anaconda installed, 'anaconda.com',

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if you have this installed, you're probably going to run

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into some problems.

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Anaconda comes with its own distribution of Python, which

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can actually compete or conflict with 'pyenv' a little bit.

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I've actually noticed that in my own experience.

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So preferably if you're going to use one, just stick with one of these.

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Now, once you have that installed, if you wanted to, you

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could just go straight to your command line here.

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Let's clear this out, and we can do 'pyenv',

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let's just type 'pyenv',

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let's see what happens. 'pyenv', 'some useful pyenv

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commands are:' - commands, local, global, shell, install, uninstall,

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rehash, version, versions, which and whence. We really only need

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a few of these. Let's do 'pyenv versions', because this one's going to list all

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the Python versions that are available on 'pyenv'.

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These are the ones that I have on my computer.

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So I currently have Python 3.5.7, 3.6.0, 3.7.2, and 3.8.0

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So if I do 'python -V', this is the version I'm using, Python 3.7.2,

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but I can now change that very easily with 'pyenv',

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and I'm going to change this across my entire system

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right now. 'pyenv global 3.5.7',

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and let's do 'python'.

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let's spell 'python' correctly, though, and look at that.

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I'm using a different version of Python now.

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And if you want to see the current version, you can literally

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just type 'python version', and it will tell you in here, not

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'python version', 'pyenv version',

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and it tells you which one you're using.

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And let's go back to, let's not go back,

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let's change our version to Python 3.8.

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So I'm going to do 'pyenv global 3.8.0',

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that's because I have that installed already.

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'pyenv versions' tells me I have it set. Now

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what happens if you want to install a new version?

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We just have to find out the version that you want, and then you can

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do 'pyenv install', and then the version name.

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Let's see what happens here.

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It'd be really great if it gave us all the version names,

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but you could effectively do 'pyenv install 3.8.0', and it will

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install it for you, and then you can use it.

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I'm actually going to go back to 3.7, because that's what

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a lot of my projects right now are using, 'pyenv global 3.7.2',

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'pyenv version', and I'm back on 3.7.2.

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Once again, there is a little bit of a conflict here.

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So if you are using Anaconda, chances are you're going to want

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to continue to use Anaconda,

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otherwise you're going to run into some pathing issues,

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and I've noticed that those issues are not the most straightforward

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problem to solve.

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But if you aren't using Anaconda, 'pyenv' is definitely a good way to go.