Chapter 29 - Installing Packages¶
When you’re first starting out as a Python programmer, you don’t think about how you might need to install an external package or module. But when that need appears, you’ll want to know how to in a hurry! Python packages can be found all over the internet. Most of the popular ones can be found on the Python Package Index (PyPI). You will also find a lot of Python packages on github, bitbucket, and Google code. In this article, we will be covering the following methods of installing Python packages:
- Install from source
- Other ways to install packages
Installing from Source¶
Installing from source is a great skill to have. There are easier ways, which we’ll be getting to later on in the article. However, there are some packages that you have to install from source. For example, to use easy_install, you will need to first install setuptools. To do that, you will want to download the tar or zip file from the Python Package Index and extract it somewhere on your system. Then look for the setup.py file. Open up a terminal session and change directories to the folder that contains the setup file. Then run the following command:
python setup.py install
If Python isn’t on your system path, you will receive an error message stating that the python command wasn’t found or is an unknown application. You can call this command by using the full path to Python instead. Here’s how you might do it if you were on Windows:
c:\python34\python.exe setup.py install
This method is especially handy if you have multiple versions of Python installed and you need to install the package to different ones. All you need to do is type the full path to the right Python version and install the package against it.
Some packages contain C code, such as C header files that will need to be compiled for the package to install correctly. On Linux, you will normally already have a C/C++ compiler installed and you can get the package installed with minimal headaches. On Windows, you will need to have the correct version of Visual Studio installed to compile the package correctly. Some people say you can use MingW too, but I have yet to find a way to make that work. If the package has a Windows installer already pre-made, use it. Then you don’t have to mess with compiling at all.
Once you have setuptools installed, you can use easy_install. You can find it installed in your Python installation’s Scripts folder. Be sure to add the Scripts folder to your system path so you can call easy_install on the command line without specifying its full path. Try running the following command to learn about all of easy_install’s options:
When you want to install a package with easy_install, all you have to do is this:
easy_install will attempt to download the package from PyPI, compile it (if necessary) and install it. If you go into your Python’s site-packages directory, you will find a file named easy-install.pth that will contain an entry for all packages installed with easy_install. This file is used by Python to help in importing the module or package.
You can also tell easy_install to install from a URL or from a path on your computer. It can also install packages directly from a tar file. You can use easy_install to upgrade a package by using -upgrade (or -U). Finally, you can use easy_install to install Python eggs. You can find egg files on PyPI and other locations. An egg is basically a special zip file. In fact, if you change the extension to .zip, you can unzip the egg file.
Here are some examples:
easy_install -U SQLAlchemy easy_install http://example.com/path/to/MyPackage-1.2.3.tgz easy_install /path/to/downloaded/package
There are some issues with easy_install. It will try to install a package before it’s finished downloading. There is no way to uninstall a package using easy_install. You will have to delete the package yourself and update the easy-install.pth file by removing the entry to the package. For these reasons and others, there was movement in the Python community to create something different, which caused pip to be born.
The pip program actually comes with Python 3.4. If you have an older version of Python, then you will need to install pip manually. Installing pip is a little bit different than what we have previously discussed. You still go to PyPI, but instead of downloading the package and running its setup.py script, you will be asked to download a single script called get-pip.py. Then you will need to execute it by doing the following:
This will install setuptools or an alternative to setuptools called distribute if one of them is not already installed. It will also install pip. pip works with CPython versions 2.6, 2.7, 3.1, 3.2, 3.3, 3.4 and also pypy. You can use pip to install anything that easy_install can install, but the invocation is a bit different. To install a package, do the following:
pip install package_name
To upgrade a package, you would do this:
pip install -U PackageName
You may want to call pip -h to get a full listing of everything pip can do. One thing that pip can install that easy_install cannot is the Python wheel format. A wheel is a ZIP-format archive with a specially formatted filename and the .whl extension. You can also install wheels via its own command line utility. On the other hand, pip cannot install an egg. If you need to install an egg, you will want to use easy_install.
A Note on Dependencies¶
One of the many benefits of using easy_install and pip is that if the package has dependencies specified in their setup.py script, both easy_install and pip will attempt to download and install them too. This can alleviate a lot of frustration when you’re trying new packages and you didn’t realize that package A depended on Packages B, C and D. With easy_install or pip, you don’t need to worry about that any more.
At this point, you should be able to install just about any package that you need, assuming the package supports your version of Python. There are a lot of tools available to the Python programmer. While packaging in Python is a bit confusing right now, once you know how to use the proper tools, you can usually get what you want installed or packaged up. We will be looking more at creating our own packages, eggs and wheels in Part V.