How do I install from a local cache with pip?

I install a lot of the same packages in different virtualenv environments. Is there a way that I can download a package once and then have pip install from a local cache?

This would reduce download bandwidth and time.

Updated Answer 19-Nov-15

According to the Pip documentation:

Starting with v6.0, pip provides an on by default cache which functions similarly to that of a web browser. While the cache is on by default and is designed do the right thing by default you can disable the cache and always access PyPI by utilizing the --no-cache-dir option.

Therefore, the updated answer is to just use pip with its defaults if you want a download cache.

Original Answer

From the pip news, version 0.1.4:

Added support for an environmental variable $PIP_DOWNLOAD_CACHE which will cache package downloads, so future installations won’t require large downloads. Network access is still required, but just some downloads will be avoided when using this.

To take advantage of this, I've added the following to my ~/.bash_profile:

export PIP_DOWNLOAD_CACHE=$HOME/.pip_download_cache

or, if you are on a Mac:

export PIP_DOWNLOAD_CACHE=$HOME/Library/Caches/pip-downloads

Notes

If a newer version of a package is detected, it will be downloaded and added to the PIP_DOWNLOAD_CACHE directory. For instance, I now have quite a few Django packages.
This doesn't remove the need for network access, as stated in the pip news, so it's not the answer for creating new virtualenvs on the airplane, but it's still great.

In my opinion, pip2pi is a much more elegant and reliable solution for this problem.

From the docs:

pip2pi builds a PyPI-compatible package repository from pip requirements

pip2pi allows you to create your own PyPI index by using two simple commands:

To mirror a package and all of its requirements, use pip2tgz:

$ cd /tmp/; mkdir package/
$ pip2tgz packages/ httpie==0.2
...
$ ls packages/
Pygments-1.5.tar.gz
httpie-0.2.0.tar.gz
requests-0.14.0.tar.gz

To build a package index from the previous directory:

$ ls packages/
bar-0.8.tar.gz
baz-0.3.tar.gz
foo-1.2.tar.gz
$ dir2pi packages/
$ find packages/
/httpie-0.2.0.tar.gz
/Pygments-1.5.tar.gz
/requests-0.14.0.tar.gz
/simple
/simple/httpie
/simple/httpie/httpie-0.2.0.tar.gz
/simple/Pygments
/simple/Pygments/Pygments-1.5.tar.gz
/simple/requests
/simple/requests/requests-0.14.0.tar.gz

To install from the index you built in step 2., you can simply use:
```
pip install --index-url=file:///tmp/packages/simple/ httpie==0.2
```

You can even mirror your own index to a remote host with pip2pi.

For newer Pip versions:

Newer Pip versions now cache downloads by default. See this documentation:

https://pip.pypa.io/en/stable/reference/pip_install/#caching

For older Pip versions:

Create a configuration file named ~/.pip/pip.conf, and add the following contents:

[global]
download_cache = ~/.cache/pip

On OS X, a better path to choose would be ~/Library/Caches/pip since it follows the convention other OS X programs use.

PIP_DOWNLOAD_CACHE has some serious problems. Most importantly, it encodes the hostname of the download into the cache, so using mirrors becomes impossible.

The better way to manage a cache of pip downloads is to separate the "download the package" step from the "install the package" step. The downloaded files are commonly referred to as "sdist files" (source distributions) and I'm going to store them in a directory $SDIST_CACHE.

The two steps end up being:

pip install --no-install --use-mirrors -I --download=$SDIST_CACHE <package name>

Which will download the package and place it in the directory pointed to by $SDIST_CACHE. It will not install the package. And then you run:

pip install --find-links=file://$SDIST_CACHE --no-index --index-url=file:///dev/null <package name>

To install the package into your virtual environment. Ideally, $SDIST_CACHE would be committed under your source control. When deploying to production, you would run only the second pip command to install the packages without downloading them.

Starting in version 6.0, pip now does it's own caching:

DEPRECATION pip install --download-cache and pip wheel --download-cache command line flags have been deprecated and the functionality removed. Since pip now automatically configures and uses it’s internal HTTP cache which supplants the --download-cache the existing options have been made non functional but will still be accepted until their removal in pip v8.0. For more information please see https://pip.pypa.io/en/latest/reference/pip_install.html#caching