# Faster PyYAML Parsing with LibYAML

This morning, Christian submitted a great pull request to speed up YAML parsing in MSMBuilder using LibYAML. In MSMBuilder, we use a YAML file to save the "project", which is keeps the path to all of the files associated with an MSMBuilder project, such as the different trajectories, and a PDB for the protein's topology.

YAML is convenient here: being easily editable plain text, it makes it pretty easy to check what's in your project, and perform simple tasks like splitting a project in two, without needing any libraries or programming. But there's one big disadvantage: it can be really really slow to load a large project file. Although it's not usually the rate limiting step, it's still really annoying.

Using the LibYAML parser (written in C) can speed up the reading significantly. To see if your python installation is linked against LibYAML, try the following command.

python -c "from yaml import CLoader"


If this blows up with an ImportError, then LibYAML isn't installed. If the commands runs just fine, then you've already got LibYAML.

## Installing LibYAML

To install LibYAML, you can either build it from source or use a package manager. If you've got sudo privileges, you can easily install LibYAML from source, following the directions from here, with:

wget http://pyyaml.org/download/libyaml/yaml-0.1.4.tar.gz
tar -xzvf yaml-0.1.4.tar.gz
cd yaml-0.1.4
./configure
make
sudo make install


If you're on a machine without sudo privileges, use a --prefix flag with configure to install the library in user-space. You'll probably also have to add the new library directory to LD_LIBRARY_PATH (or DYLD_LIBRARY_PATH on mac).

If you access to a package manager like apt-get on ubuntu, then you can install LibYAML with the command sudo apt-get install libyaml-dev. On a centos system, you should be able to get LibYAML with sudo yum install libyaml-devel.

## Rebuilding PyYAML with the C Bindings

If you've installed LibYAML with the default location (either by compiling from source without --prefix, or using your package manager), then you can rebuild PyYAML with the LibYAML bindings by just reinstalling it through pip with pip install pyyaml --upgrade --force.

Otherwise, download the source package from pypi and edit the setup.cfg file to point to the lib and include directories of your LibYAML installation. I configured LibYAML with --prefix=\$HOME/opt/yaml, so uncommented lines 7 and 10 of setup.cfg, and edited them to read

# List of directories to search for 'yaml.h' (separated by ':').
include_dirs=/usr/local/include:../../include:/home/rmcgibbo/opt/yaml/include

# List of directories to search for 'libyaml.a' (separated by ':').
library_dirs=/usr/local/lib:../../lib:/home/rmcgibbo/opt/yaml/lib


And then rebuilt the package with

python setup.py --with-libyaml install