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In addition to the modules that distribute with Python in the Python

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standard library there is also a repository of modules that have been

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written by other people.

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This is called PyPI, the Python Package Index, and it's available at this web page.

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We're going to click on the link here, Python 3 packages, so we can see what

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packages are available that support Python 3.

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Of course by the time you look at this, this list will probably be much longer

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because more-and-more modules are being imported to Python 3 all the time.

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Just as an example of how to install a module that you find here, I've selected

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one called bitstring, and what this does is it allows you an easy way of working

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with strings of bits, and we'll go ahead and we'll download this and install it.

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And so this is the page and most of the pages look something like this.

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They've got some documentation.

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They have a link to the web site where it's been developed and a way to download a module.

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And so I've already downloaded this and unpacked it on the computer here and there it is.

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Go ahead and change into that directory.

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And we can see that it's this Python file and a setup.py and some other related files.

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All of the modules that are available on PyPI have a setup.py and it's a

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standard, and so they all install pretty much the same way.

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Now I am installing this on Windows.

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And the way that you install it on other operating systems is pretty

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much exactly the same.

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You run the setup.py script with the argument install.

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And on Windows, unless you've put Python in your path you'll have to type in

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the path to Python.

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On most other systems you won't need to do that.

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So I am just going to type in the path here.

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And I say python31, which is the standard place where it installs on a Windows system.

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And let's say python, and then I am going to give the name of the setup script,

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which is setup.py and the word install, like that.

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And so if you are on a UNIX-based system like a Mac or Linux you probably just

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type something like Python 3 setup.py install.

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You do want to make sure that if you have both Python 3 and an earlier version

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of Python installed on your system that you are running the correct Python when

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you run the setup.py.

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If for example you were to run Python 2 and the setup and install,

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your module would be installed in the path for the Python 2 and not in the

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path for the Python 3.

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So you want to make sure you are running the right Python when you do this.

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And so in this case that's by using this directory and then Python and

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setup.py and install.

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So I am going to go ahead and run that, and there it is it's built it and it's

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copied it into the site-packages directory, which is where all of your user

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installable packages are installed.

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And again if you are on a UNIX system or on any different operating system that

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will be in a different place, but it'll be called site-packages just like that.

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Let me go ahead and change to that directory so we can see what happens here.

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So this is the site-packages directory on this system, and you see it just has

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this one module installed.

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And it installs this egg-info, which is just a lot of information about the

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module, and that's useful.

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It installs the .py file and then it also installs this .pyc file.

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What that is is a complied version of the module.

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So that when it's run it's actually a little bit more efficient, and this

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happens at install time.

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So we'll go ahead and switch to Eclipse now and we'll take a look at how we use this.

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Make a working copy of modules.py. Call that modules-working.py.

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We'll open that up and instead of import sys here we are going to import

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bitstring, and we'll go ahead and use it. Set a variable.

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Now I have already read the documentation from the module.

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That might be the first thing that you'll want to do. a = bitstring.BitString(bin =

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01010101, and I want to put that in quotes because that's a string.

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So what this does is it allows you to find binary patterns using strings

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and then use those.

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We'll go ahead and print it in some different forms. a.hex, a.bin, a.unsigned

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integer, and we'll save that and run it.

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And there we have successfully installed and used a module that we've found on the PyPI index.

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So the PyPI index is a very useful thing and you want to be careful of course

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because a lot of people submit modules and they are varying quality, so you

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want to do a little bit of vetting.

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Or you may just want to download some modules and look at their source code and

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learn how other people do things.

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It's a very valuable resource.

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And again it gives you the opportunity to leverage other people's work and to

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not be reinventing the wheel.

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So do take a look at the Python index at PyPI and become familiar with what it

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is and how it works and add it to your quiver of tools.