Transition-based statistical parser
Python Shell
Latest commit 9122f30 Jan 4, 2016 @syllog1sm * Add pin for murmurhash



This library is research code, and is in maintainence mode.

For my actively developed, commercially-focussed NLP library, see

Redshift is a natural-language syntactic dependency parser. The current release features fast and accurate parsing, but requires the text to be pre-processed. Future releases will integrate tokenisation and part-of-speech tagging, and have special features for parsing informal text.

If you don't know what a syntactic dependency is, read this:

Main features:

  • Fast linear time parsing: the slowest model is still over 100 sentences/second
  • State-of-the-art accuracy: 93.5% UAS on English (Stanford scheme, WSJ 23)
  • Super fast "greedy" mode: over 1,000 sentences per second at 91.5% accuracy
  • Native Python interface (the parser is written in Cython)

Key techniques:

  • Arc-eager transition-based dependency parser
  • Averaged perceptron for learning
  • redshift.parser.BeamParser is basically the model of Zhang and Nivre (2011)
  • redshift.parser.GreedyParser adds the non-monotonic model of Honnibal et al (2013) to the dynamic oracle model of Goldberg and Nivre (2012)
  • redshift.features includes the standard Zhang and Nivre (2011) feature set, and also some work pending publication.

Example usage

Here is an example of how the parser is called from Python, once you have a model trained:

>>> import redshift.parser
>>> from redshift.sentence import Input
>>> parser = redshift.parser.Parser(<model directory>)
>>> sentence = Input.from_untagged(['A', 'list', 'of', 'tokens', 'is', 'required', '.'])
>>> parser.parse(sentence)
>>> print sentence.to_conll()

The command-line interfaces have a lot of probably-confusing options for my current research. The main scripts I use are scripts/, scripts/, and scripts/ . All print usage information, and require the plac library.

From a Unix/OSX terminal, after compilation, and within the "redshift" directory:

$ export PYTHONPATH=`pwd`
$ ./scripts/ # Use -h or --help for more detailed info. Most of these are research flags.
usage: [-h] [-a static] [-i 15] [-k 1] [-f 10] [-r] [-d] [-u] [-n 0] [-s 0] train_loc model_loc error: too few arguments
$ ./scripts/ -k 16  <CoNLL formatted training data> <output model directory>
$ ./scripts/ <model directory produced by> <input> <output_dir>
$ ./scripts/ output_dir/parses <gold file>

In more detail:

  • Ensure your PYTHONPATH variable includes the redshift directory
  • Most of the training-script flags refer to research settings.
  • the k parameter controls the speed-accuracy trade-off, via the beam-width. Run-time is roughly O(nk), where n is the number of words, and k is the beam-width. In practice it's slightly sub-linear in k due to some simple memoisation. Accuracy plateaus at about k=64. For k=1, use "-a dyn -r -d", to enable some recent special-case wizardry that gives the k=1 case over 1% extra accuracy, at no run-time cost.
  • reads in the training configuration from "parser.cfg", which sits in the output model directory.
  • The parser currently expects one sentence per line, space-separated tokens, tokens of the form word/POS.
  • runs as a separate script from so that the parser never sees the answers, and cannot "accidentally cheat".


The following commands will set up a virtualenv with Python 2.7.5, the parser, and its core dependencies from scratch:

$ git clone
$ cd redshift
$ git checkout develop

a) $ virtualenv .env
b) $ ./ # Downloads Python 2.7.5 and virtualenv

$ source .env/bin/activate
$ pip install distribute
$ pip install cython
$ pip install thinc
$ pip install -r requirements.txt
$ export PYTHONPATH=`pwd`:$PYTHONPATH # ...and set PYTHONPATH.
$ fab make test

The script downloads and compiles Python 2.7.5, and uses it to create a virtualenv. This is one way to use a version of Python that isn't system-wide, or to control the compiler that Cython will use. You may not need to do this, or you may wish to do it manually --- it's up to you.

virtualenv is not a requirement, although it's useful. If a virtualenv is not active (i.e. if the $VIRTUALENV environment variable is not set), you'll need to ensure that the file knows where to find the C headers that the murmurhash dependency installs.

Installation requires a recent version of pip, which is provided by the version of virtualenv that the script downloads. If you don't use the script, ensure you're using a recent version of pip.


redshift is written almost entirely in Cython, a superset of the Python language that additionally supports calling C/C++ functions and declaring C/C++ types on variables and class attributes. This allows the compiler to generate very efficient C/C++ code from Cython code. Many popular Python packages, such as numpy, scipy and lxml, rely heavily on Cython code.

A Cython source file such as redshift/parser.pyx is compiled into redshift/parser.cpp and redshift/ by the project's file. The module can then by imported by standard Python code, although only the pure-Python functions (declared by "def" and "cpdef", instead of "cdef") will be accessible.

The parser currently has Cython as a requirement, instead of distributing the "compiled" .cpp files as part of the release (against Cython's recommendation). This could change in future, but currently it feels strange to have a "source" release that users wouldn't be able to modify.


This software is available for non-commercial use only. You may download, run and modify the code for research purposes, personal interest, education, teaching, etc. My commercial NLP suite is spaCy: .

Copyright (C) 2014 Matthew Honnibal