Pip is an installer for Python packages written by Ian Bicking. It can install packages, list installed packages, upgrade packages, and uninstall packages.
We’ll be using virtualenv so our installation experiments are contained and don’t modify your system Python environment. If you aren’t already familiar with virtualenv, you may want to read up on it first.
Create a virtualenv:
virtualenv --no-site-packages pip_test_env
We use the --no-site-packages flag to prevent this virtualenv from “seeing” your global Python “site-packages” directory, so that our experiments aren’t confused by any Python packages you happen to already have installed globally.
Recent versions of virtualenv (1.4+) automatically install pip for you inside the virtualenv (there will already be a pip script in pip_test_env/bin/). If you are using a pre-1.4 virtualenv, run pip_test_env/bin/easy_install pip to install pip in the virtual environment.
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If you are using Windows, executable scripts in the virtualenv will be located at pip_test_env\Scripts\ rather than pip_test_env/bin/. Just replace all occurrences of the latter with the former.
Let’s “activate” the virtualenv to put pip_test_env/bin on our default PATH, so we can just type pip instead of pip_test_env/bin/pip:
. pip_test_env/bin/activate
On Windows, this is:
pip_test_env\Scripts\activate.bat
In either case, your shell prompt should now begin with (pip_test_env) to remind you that a virtualenv is activated. When you are done working with this virtualenv type deactivate to remove its bin directory from your PATH.
Let’s install the Markdown package:
pip install Markdown
Markdown is now installed; you can import and use it:
python -c "import markdown; print markdown.markdown('**Excellent**')"
(Because your virtualenv is activated, python runs the virtualenv’s python binary in pip_test_env/bin/python.)
Its command-line script is installed in pip_test_env/bin/markdown (or pip_test_env\Scripts\markdown.bat).
The rest of Markdown’s files are installed in pip_test_env/lib/python2.X/site-packages/markdown (where 2.X is your Python version), and the metadata describing what has been installed is in pip_test_env/lib/pythonx.x/site-packages/Markdown-2.0.3-py2.X.egg-info/.
To list installed packages and versions, use the freeze command:
pip freeze
Pip will give you a listing something like this:
Markdown==2.0.3
wsgiref==0.1.2
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The wsgiref package is a part of the Python standard library. Currently it is the only standard library package that includes package metadata, so it is the only standard library package whose presence pip reports.
You can also give pip a version specifier for a package using one or more of ==, >=, >, <, <=:
pip install 'Markdown<2.0'
This will find your current installation of Markdown 2.0.3, automatically uninstall it, and install Markdown 1.7 (the latest version in the 1.x series) in its place. You can even combine version specifiers with a comma:
pip install 'Markdown>2.0,<2.0.3'
If you want to upgrade a package to its most recent available version, use the -U or --upgrade flag:
pip install -U Markdown
Now let’s uninstall Markdown:
pip uninstall Markdown
After showing you which files/directories will be removed and requesting confirmation, pip will uninstall everything installed by the Markdown package.
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Pip inside a virtualenv will only uninstall packages installed within that virtualenv. For instance, if you try to pip uninstall wsgiref it will refuse, because the virtualenv references the global Python’s standard library, so the wsgiref package is not installed within the virtualenv.
How does pip know what to install when you run pip install Markdown? By default, it checks the Python Package Index (or PyPI) for a package of that name. In this case, it found one; but what if you want to install a package that hasn’t been uploaded to PyPI?
You have several options:
You can install directly from a tarball or zip file, as long as there is a working setup.py file in the root directory of the unzipped contents:
pip install path/to/mypackage.tgz
You can also install from a tarball/zip file over the network:
pip install http://dist.repoze.org/PIL-1.1.6.tar.gz
Using the --editable or -e option, pip has the capability to install directly from a version control repository (it currently supports Subversion, Mercurial, Git, and Bazaar):
pip install -e svn+http://svn.colorstudy.com/INITools/trunk#egg=initools-dev
This option shells out to the commandline client for each respective VCS, so you must have the VCS installed on your system. The repo URL must begin with svn+ (or hg+, git+, or bzr+) and end with #egg=packagename; otherwise, pip supports the same URL formats and wire protocols supported by the VCS itself.
Pip will checkout the source repo into a src/ directory inside the virtualenv (i.e. pip_test_env/src/initools-dev), and then run python setup.py develop in that source repo. This “links” the code directly from the repo into the virtualenv’s site-packages directory (by adding the repo directory into easy-install.pth), so changes you make in the source checkout are effective immediately.
If you already have a local VCS checkout you want to keep using, you can just use pip install -e path/to/repo to install it “editable” in the same way.
You can use the -f or --find-links option to add another URL pip should search for links to the package. If you dump some package tarballs in a webserver directory and turn on automatic indexing, you can point pip at that index page and install any of those packages, assuming you named the files in the pattern packagename-version.ext.
For example, if you upload a tarball MyApp-1.0.tgz to a my-packages directory on your webserver, and make sure indexing is on for that directory, you can run:
pip install MyApp -f http://www.example.com/my-packages/
If you want more of the features provided by PyPI (including the ability to upload packages with python setup.py sdist upload), you can run software such as chishop, which implements the PyPI API, on your own server. Then you can use pip’s -i (or --index-url) or --extra-index-url options to point it at your index.
For instance, if you set up your own index at http://www.example.com/chishop/, you might run:
pip install MyPrivateApp -i http://www.example.com/chishop/simple/
If you use -i pip won’t check PyPI, only the index you provide. If you are installing multiple packages at once, some from your index and some from PyPI, you may want to use --extra-index-url instead, so pip will check both indexes.
See the pip documentation for a good overview.