Installing pysam

Pysam provides a python interface to the functionality contained within the htslib C library. There are two ways that these two can be combined, builtin and external.


The typical installation will be through pypi_:

pip install pysam

This will compile the builtin htslib source code within pysam.

htslib can be configured at compilation to turn on additional features such support using encrypted configurations, enable plugins, and more. See the htslib project for more information on these.

Pysam will attempt to configure htslib to turn on some advanced features. If these fail, for example due to missing library dependencies (libcurl, libcrypto), it will fall back to conservative defaults.

Options can be passed to the configure script explicitely by setting the environment variable HTSLIB_CONFIGURE_OPTIONS. For example:

export HTSLIB_CONFIGURE_OPTIONS=--enable-plugins
pip install pysam


pysam can be combined with an externally installed htslib library. This is a good way to avoid duplication of libraries. To link against an externally installed library, set the environment variables HTSLIB_LIBRARY_DIR and HTSLIB_INCLUDE_DIR before installing:

export HTSLIB_LIBRARY_DIR=/usr/local/lib
export HTSLIB_INCLUDE_DIR=/usr/local/include
pip install pysam

Note that the location of the file needs to be known to the linker once you run pysam, for example by setting the environment-varirable LD_LIBRARY_PATH.


pysam depends on cython to provide the connectivity to the htslib C library. The installation of the source tarball (.tar.gz) python 2.7 contains pre-built C-files and cython needs not be present during installation. However, when installing the source tarball on python 3 or building from the repository, these pre-built C-files are not present and cython needs to be installed beforehand.