So virtual env is a tool that lets us have separate worlds of python libraries for

separate projects.

So for instance,

right now I am in a thing called new project, super duper creative name.

And so I want to make a new virtual env so that I can install my stuff here for

new project, so it doesn't conflict with old project.

Normally when you install something with Pip, it gets installed to

a global repository of libraries, usually called site packages.

But what if you do one project with Django 1.8, and

your next project is with Django 1.9?

You'd have to make sure that your 1.8 project still works with

1.9 once you upgrade.

Or you'd have to decide not to use Django 1.9.

You'd have to decide not to upgrade and just build everything with Django

1.8 from now on forever and ever because you never upgrade.

Or for the best of all the worlds, you use virtual env for

each of your projects and you just install whatever that project needs.

Now, back in the days of Python 2, and even the first couple of versions of

Python 3, you had to install a separate tool to use virtual env.

So you'd see instructions like pip3 install virtualenv.

But as of Python 3.3,

virtual env has actually been merged into the Python standard library.

So now you can use it without having to install anything.

This is awesome.

So how do we create a virtual env?

So I've gone ahead and I've made a place to do my treehouse Python learning.

I'm just inside of documents and I've what is it, where am I?

Whatever.

Anyway, I'm inside of [LAUGH], you can see I went into documents and

I just made a folder called, new project.

You know, maybe you'd wanna do like treehouse, and

then let's move idle and new project inside treehouse.

Alright so, maybe you'd want to do that.

And I'm gonna pretend that I'm about to start on the flash basics course.

Maybe you're already done with that course, maybe you haven't started it yet

or you know, or maybe you did it or

you're going to do it in workspaces and that's a great idea.

Let's make a directory for our course.

You do this for each of your projects too.

Maybe you're building a library website or

something, you'd make a directory for that.

So we're going to make a directory for flask basics and we're gonna go in there.

And now, let's clear my screen.

Now I need to make the virtual env.

I can call the virtual env anything I want, but

generally you want to avoid the names of libraries that you're likely to install,

or the virtual env module itself, which is actually named VEMV.

So this is for flash basics, I'm going to use the initials fb.

So python three dash mvemv.

And now it expects a name.

We're gonna put in fb.

So that dash m flag, this thing right here,

that actually tells Python to use a particular module.

Modules have or can have a bit of special code written in them that when they're

used this way, which the venv module has of course, it knows what to do.

It has like a special invocation.

So what this does is it expects the name of a virtual env to create,

which it got and then it creates a virtual env using that.

So if we look, we'll see here that we have fb, and

if we do ls of fb, then we see the virtual env bits and pieces.

Now we don't want to make our code inside of fb.

This is where libraries get installed too.

We don't want to write our own code in there.

The reason is because at any point, I should be able to just do that.

And that, and other than installing some packages, I'm right back to normal.

Nothing's new.

OK, now, before we can use the virtual env, we have to activate it.

So we'll do source fb, then activate, and that's it.

It's activated.

I know it's activated because I have this little parentheses fb parentheses

over here, and that says hey you're working in the fb virtual env.

Which, for

example if I do which Python you see that it's the Python inside fb bin.

Right?

It's not one way on the outside.

And if I do Python version, it's 3.5.

So even though it was Python 3 outside of the virtual env,

inside the virtual env it's just Python.

And now if I want to install things I can just use pip to install them.

So we'll do pip install Flask, which is the thing I'm probably gonna need for

Flask basics.

And it downloads and installs this stuff.

And I just go on making code like I normally would,

just like the course tells me to.