You could try the search feature in pip:
$ pip search yaml
which looks for packages in PyPI with yaml in the short description that reveals various packages including PyYaml, yamltools, and PySyck, among others .
Now you know a specific package name you can install it:
$ pip install pyyaml
If you want to install python yaml system-wide in linux, you can also use a package manager, like aptitude or yum:
$ sudo apt-get install python-yaml
$ sudo yum install python-yaml