AllegroGraph Python API

The AllegroGraph Python API offers convenient and efficient access to an AllegroGraph server from a Python-based application. This API provides methods for creating, querying and maintaining RDF data, and for managing the stored triples. The AllegroGraph Python API deliberately emulates the Eclipse RDF4J (formerly Aduna Sesame) API to make it easier to migrate from RDF4J to AllegroGraph. The AllegroGraph Python API has also been extended in ways that make it easier and more intuitive than the RDF4J API.

Requirements

Python versions 2.7+ and 3.5+ are supported. The installation method described here uses the pip package manager. On some systems this might require installing an additional package (e.g. python-pip on RHEL/CentOS systems). All third-party libraries used by the Python client will be downloaded automatically during installation.

See also the Optional requirements section below.

Installation

Important

It is highly recommended to perform the install in a virtualenv environment.

The client can be installed from PyPI using the pip package manager:

pip install agraph-python

Alternatively, a distribution archive can be obtained from ftp://ftp.franz.com/pub/agraph/python-client/ and installed using pip:

pip install agraph-python-<VERSION>.tar.gz

Warning

Python 2.6 users should consider installing the simplejson package:

pip install simplejson

since the built-in JSON module in that version of Python offers unsatisfactory performance. The AllegroGraph Python client will detect and use simplejson automatically if it is installed.

Offline installation

If it is not possible to access PyPI from the target machine, the following steps should be taken:

• In a compatible environment with unrestricted network access run:

  pip wheel agraph-python
  

• If desired do the same for optional dependencies:

  pip wheel pycurl simplejson
  

• This will generate a number of .whl files in the current directory. These files must be transferred to the target machine.

• On the target machine use this command to install:

  pip install --no-index --find-links=<DIR> agraph-python
  

  where <DIR> is the directory containing the .whl files generated in the previous step.

Testing

To validate the installation make sure that you have access to an AllegroGraph server and run the following Python script:

from franz.openrdf.connect import ag_connect
with ag_connect('repo', host='HOST', port='PORT',
                user='USER', password='PASS') as conn:
    print (conn.size())

Substitute appropriate values for the HOST/PORT/USER/PASS placeholders. If the script runs successfully a new repository named repo will be created.

Proxy setup

It is possible to configure the AllegroGraph Python client to use a proxy for all its connection to the server. This can be achieved by setting the AGRAPH_PROXY environment variable, as in the following example:

# Create a SOCKS proxy for tunneling to an internal network
ssh -fN -D 1080 [email protected]
# Configure agraph-python to use this proxy
export AGRAPH_PROXY=socks://localhost:1080

The format of the AGRAPH_PROXY value is TYPE://HOST:PORT, where TYPE can be either http, socks4, socks5 or socks (a synonym for socks5). Note that if a SOCKS proxy is used, DNS lookups will be performed by the proxy server.

Unit tests

The Python client includes a suite of unit tests that can be run after installation. The tests are executed using the pytest framework and also use a few utilities from nose, so these two packages have to be installed. We also need the pytest-mock plugin:

pip install pytest pytest-mock nose

The tests require a running AllegroGraph server instance. The configuration of this server is passed to the tests through environment variables:

# Host and port where the server can be reached. These values are the
# default, it is only necessary to define the variables below if your
# setup is different
export AGRAPH_HOST=localhost
export AGRAPH_PORT=10035

# Tests will create repositories in this catalog.
# It must exist on the server. Use "/" for the root catalog.
export AGRAPH_CATALOG=tests

# Login credentials for the AG server.
# The user must have superuser privileges.
export AGRAPH_USER=test

# Use a prompt to read the password
read -s -r -p "Password for user ${AGRAPH_USER}: " AGRAPH_PASSWORD
export AGRAPH_PASSWORD

To run the tests, type:

pytest --pyargs franz.openrdf.tests.tests --pyargs franz.openrdf.tests.newtests

Optional requirements

The Python client can utilize a few additional third-party libraries if these are available on the host system:

• pycurl: can be used as the HTTP backend. It might offer better performance than requests (the default backend).
• simplejson: recommended for Python 2.6 users to significantly improve performance. Has negligible impact on other Python versions.

These can be downloaded and installed from PyPI:

pip install pycurl
pip install simplejson

Since the packages discussed here use native extensions, it is necessary to have a proper development environment set up so that the compilation may succeed. This environment must include:

• A C compiler
• Python development headers
• libcurl development headers

Below we describe more detailed setup instructions for some of the supported systems.

Windows

The required packages are available in binary form for Windows, so it is not necessary to install any compilers or headers.

RHEL 6/7 and compatible systems

On RHEL-like systems the requirements mentioned above can be satisfied by following these steps (note that root privileges are required):

• Enable EPEL repositories, since some of the required packages are only available there. The detailed instructions can be found here. On CentOS systems, simply run:

  yum -y install epel-release
  

• Install the required packages:

  yum -y install python-devel python-pip libcurl-devel gcc
  

• Before installing the AllegroGraph Python client make sure that the following environment variable is set:

  export PYCURL_SSL_LIBRARY=nss
  

• To use virtual environments (recommended) an additional package is needed:

  yum -y install python-virtualenv
  

Ubuntu

The following packages are required to use the client with Python 2:

apt-get install python-pip libcurl-gnutls libcurl4-gnutls-dev libgnutls28-dev

For Python 3 this becomes:

apt-get install python3-pip libcurl-gnutls libcurl4-gnutls-dev libgnutls28-dev

Note

Using different SSL backends.

Ubuntu offers three variants of curl, built using different SSL libraries. These variants differ in their licensing and SSL related capabilities (see https://curl.haxx.se/docs/ssl-compared.html for more details). The instructions above use the GnuTLS version. In most cases this is an acceptable choice, but it is possible to use a different SSL implementation by installing appropriate packages before installing the AllegroGraph Python client.

To use the OpenSSL backend in curl:

apt-get install libcurl4-openssl-dev libssl-dev

For GnuTLS:

apt-get install libcurl4-gnutls-dev libgnutls28-dev

For NSS:

apt-get install libcurl4-nss-dev libnss3-dev

Note that if the client has already been installed it is necessary to reinstall the pycurl package in order to switch SSL backends:

# Uninstall old package
pip uninstall pycurl

# Reinstall, ignoring PIP cache (to force recompilation)
pip install --no-cache-dir pycurl

Arch Linux

On Arch the following packages are needed to use the client with Python 2:

pacman -S gcc python2 python2-pip libcurl

For Python 3 use:

pacman -S gcc python python-pip libcurl

Troubleshooting

If you see an error similar to the following:

ImportError: pycurl: libcurl link-time ssl backend (nss) is
different from compile-time ssl backend (none/other)

Perform this procedure (replacing <VERSION> with the actual version):

# Uninstall pycurl:
pip uninstall pycurl

# Set the required compile-time option for pycurl
export PYCURL_SSL_LIBRARY=nss

# Reinstall, but ignore cached packages (force recompile)
pip install --no-cache-dir agraph-<VERSION>-python-client.tar.gz