Modern Python Projects Transcripts
Chapter: Python versions and packages
Lecture: The problem with pip
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You often hear that Python comes with batteries included. This means that it comes with plenty of packages already installed.
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This is called the Standard Python Library. You can Goto Python Modules Index website,
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and here you can find the list of all the packages that comes with Python. So, without installing anything, you can just import them in your code.
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But what makes Python truly amazing is the Python Package Index. This list of over 260,000 packages created by other developers.
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If you find the module that you want to use, all you need to do is to run pip,
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install and the modules name, and this will download and install that package for you
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Now you could import this module in your code and start using any function that this module offers. With so many Python packages,
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you can quickly built a pretty advanced projects simply by combining different packages together. However, pip has one big problem.
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You can only have one version of a given package installed on your computer. Whenever you ask it to install a specific version of a Python package,
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it will uninstall the previous versions from your computer and installed the one that you asked for. Let me show you an example of what I mean.
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Let's say you are a Web developer and you want to build a Django website,
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so, you create a folder for the application and then you start by installing the latest version of Django with pip install Django Command.
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As you can see it, this installs Django 3. Everything works great. You build an awesome website and it's actually so good that soon
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you get a customer coming to you and asking to fix their Django website.
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Their Django website is still running on Django to so you go out from this folder
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you create a new one and then you installed Django 2 by specifying pip install django==2.2 Let's say, pip does what you ask for,
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and after a few seconds you start working on your client's website using Django 2.2. So far, so good. But later that day,
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you discover a bug on your personal website, the one that you created with Django 3.
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You quickly fix the code, but when you want to test that is working correctly you get error message saying that Django 2 is not installed.
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What? Wait. But we just installed a few days ago, where did it go? Well, when we told pip to install Django 2.2 pip first checked if we already
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have Django install and we did. But it was not the 2.2 version, so pip uninstalled that version and installed the correct one.
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As you can see here, it says uninstalling Django 3 and successfully installed Django 2. And if we check the list of packages installed on our computer,
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you will see that we no longer have Django 3. So, we just run into a problem with dependencies management.
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All the Python packages that you install with pip are called dependencies because the projects you
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are building depends on them. pip installs those dependencies in the site packages folder and
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puts each package in a separate folder named after the package. So, when we installed Django 3, it was placed in site packages/django folder.
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But when we tried to install Django 2, it was also placed in the same folder,
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so, pip has the first remove what's inside the Django folder and then install different version
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of Django. If you're only working with one Python project on your computer, then you are probably not affected by this problem.
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But sooner or later you will need to install a different version of a package,
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and you're going to run into issues with pip uninstalling some previous dependencies. Dependencies management problems are not specific.
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to Python. Basically, any programming language that allows installing external modules have to face
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this issue, and different programming languages solve it in a different way.
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For example, developers who used Ruby on rails install their packages with a tool called bundler. And when Bundler installs a new dependency,
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it puts it in a folder called Package Name-Version. So it's possible to have two different versions of a package.
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For example, here you can see we have active support 5.2.3 and 6.0 6.0.2.1 and so on. JavaScript or, more specifically, node.
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So, the server side version of JavaScript solves this problem by installing all the dependencies inside
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the folder called node modules inside of your project.
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So, each different project on your computer has a different folder where the dependencies are stored
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right now, in Python pip doesn't have a good solution for this problem.
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However, there is a proposal to use a local packages directory in the same manner as JavaScript developers do. If it gets implemented,
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pip would be installing all the dependencies in the folder inside of your project, not globally. This proposal is still draft,
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but maybe in a future version of Python problem with dependencies will be solved.
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But for now, most Python developers solved this problem using virtual environments.