rdflib-hdt 1.0

A Store back-end for rdflib to allow for reading and querying HDT documents

Read and query HDT document with ease in Python

Online Documentation

Requirements

• Python version 3.6.4 or higher

• pip

• gcc/clang with c++11 support

• Python Development headers > You should have the Python.h header available on your system. > For example, for Python 3.6, install the python3.6-dev package on Debian/Ubuntu systems.

Then, install the pybind11 library

pip install pybind11

Installation

Installation in a virtualenv is strongly advised!

Pip install (recommended)

pip install hdt

Manual installation

git clone https://github.com/Callidon/pyHDT
cd pyHDT/
./install.sh

Getting started

from hdt import HDTDocument

# Load an HDT file.
# Missing indexes are generated automatically, add False as the second argument to disable them
document = HDTDocument("test.hdt")

# Display some metadata about the HDT document itself
print("nb triples: %i" % document.total_triples)
print("nb subjects: %i" % document.nb_subjects)
print("nb predicates: %i" % document.nb_predicates)
print("nb objects: %i" % document.nb_objects)
print("nb shared subject-object: %i" % document.nb_shared)

# Fetch all triples that matches { ?s ?p ?o }
# Use empty strings ("") to indicates variables
triples, cardinality = document.search_triples("", "", "")

print("cardinality of { ?s ?p ?o }: %i" % cardinality)
for triple in triples:
  print(triple)

# Search also support limit and offset
triples, cardinality = document.search_triples("", "", "", limit=10, offset=100)
# etc ...

Handling non UTF-8 strings in python

If the HDT document has been encoded with a non UTF-8 encoding the previous code won’t work correctly and will result in a UnicodeDecodeError. More details on how to convert string to str from c++ to python here

To handle this we doubled the API of the HDT document by adding:

• search_triples_bytes(...) return an iterator of triples as (py::bytes, py::bytes, py::bytes)

• search_join_bytes(...) return an iterator of sets of solutions mapping as py::set(py::bytes, py::bytes)

• convert_tripleid_bytes(...) return a triple as: (py::bytes, py::bytes, py::bytes)

• convert_id_bytes(...) return a py::bytes

Parameters and documentation are the same as the standard version

from hdt import HDTDocument

 # Load an HDT file.
 # Missing indexes are generated automatically, add False as the second argument to disable them
document = HDTDocument("test.hdt")
it = document.search_triple_bytes("", "", "")

for s, p, o in it:
  print(s, p, o) # print b'...', b'...', b'...'
  # now decode it, or handle any error
  try:
    s, p, o = s.decode('UTF-8'), p.decode('UTF-8'), o.decode('UTF-8')
  except UnicodeDecodeError as err:
    # try another other codecs
    pass