This page gives a high-level overview of the Linguistica 5 codebase. If you are from the Linguistica 5 project group, the page For developers provides the technical notes.

Structure of the project repository

The Linguistica 5 codebase is hosted at The codebase can be concretely considered as a directory containing several components:

Developers of the Linguistica project shall consult the page For developers for set-up and workflow.


How does the Linguistica 5 code work in general? We get a good sense of it by understanding how the code gets us a dictionary of signatures to stems:

>>> import linguistica as lxa
>>> from linguistica.datasets import brown
>>> lxa_object = lxa.read_corpus(brown)
>>> sigs_to_stems = lxa_object.signatures_to_stems()

This overview walks through what happens under the hood when this code snippet is run.

brown is a string which is the path pointing to the Brown corpus that comes with the Linguistica 5 library on your local disk.

lxa_object (created by lxa.read_corpus(brown)) is an instance of the class Lexicon defined in linguistica/ Lexicon has many methods, one of which is signatures_to_stems().

What is the magic behind lxa_object.signatures_to_stems() which returns a dict of signatures to stems? The answer lies in the design of the class Lexicon. Given the definition of the class is fairly long, we will examine it step by step, unfolding only the relevant bits as we move along:

class Lexicon:

    def __init__(self, ...):


    def _initialize(self):

        # signature-related objects
        self._signatures_to_stems = None

When we create a Linguistica object by the line lxa_object = lxa.read_corpus(brown), an instance of the class Lexicon is created. When this instance is created, __init__() is called. __init__() initializes several attributes (those in the form of self.X) and triggers the method _initialize().

What does _initialize() do? It initializes all objects of interest. Most of them are initialized as None, like _signatures_to_stems as shown here. Very soon we will see why we need _signatures_to_stems (named with a leading underscore so that it is a private attribute), and why it is default to None.

Now that all initialization work is done and lxa_object is ready in the memory, we examine what happens when the final line sigs_to_stems = lxa_object.signatures_to_stems() in the code snippet is run.

When lxa_object.signatures_to_stems() is called, the method signatures_to_stems() of the Lexicon class is called. What does this method do? Let’s check out the code:

class Lexicon:

    def signatures_to_stems(self):
        Return a dict of morphological signatures to stems.

        :rtype: dict(tuple(str): set(str))
        if self._signatures_to_stems is None:
        return self._signatures_to_stems

    def _make_all_signature_objects(self):
        self._stems_to_words = signature.make_stems_to_words(
            self.wordlist(), self.parameters_['min_stem_length'],
            self.parameters_['max_affix_length'], self.parameters_['suffixing'],

        self._signatures_to_stems = signature.make_signatures_to_stems(
            self._stems_to_words, self.parameters_['max_affix_length'],
            self.parameters_['min_sig_count'], self.parameters_['suffixing'])


When signatures_to_stems() is called, an if statement is first executed. The condition of this if statement, self._signatures_to_stems is None, evaluates to True, because self._signatures_to_stems has just been initialized to be None. Then self._make_all_signature_objects() is executed (more on this below). When it finishes, self._signatures_to_stems holds the expected dict (no longer None) and is returned. (If signatures_to_stems() is called again, self._signatures_to_stems is not None anymore and the expensive computation at self._make_all_signature_objects() is avoided. This explains why in general the Linguistica 5 code has the distinction between the private attribute self._x and the public method self.x() for most objects of interest).

So, what is the method self._make_all_signature_objects()? As its name suggests, it makes all signature-related self._x. In the code shown above, two of these self._x are shown, including self._signatures_to_stems. The order by which these self._x is computed matters, because there is dependency among them. For example, self._signatures_to_stems depends on self._stems_to_words just computed in the same method.

We are potentially interested in many of the intermediate objects for research purposes. In our example, self._stems_to_words is intermediate for the computation of self._signatures_to_stems, but we expose it (by making it self._x as well as allowing the self.x() API access) because a mapping from stems to words is of interest.

To compute self._x in _make_all_signature_objects(), many function calls in the form of signature.make_x() are made. Here, signature refers to the imported module, and all the function calls make_x() are defined in linguistica/

So this is essentially how objects of interest are created via the Lexicon class. They are initialized in some way and are not actually computed until necessary. Once computed, they are available in memory for immediate retrieval. All heavy lifting is only called but not done within the class Lexicon – the real work is done in the respective modules such as signature, manifold, and so on.

Notes on the graphicsl user interface (GUI):

  • The GUI is Python 3 only. The main reason is tha the GUI requires PyQt5 (and SIP), and PyQt5 appears to be Python 3 only (at least officially?).
  • Because SIP and PyQt5 are required for the GUI but their installation is possibly non-trivial. They are designated as optional dependencies for Linguistica 5 (the GUI is not an absolute must-have for Linguistica 5 to work).
  • The GUI code is in linguistica/gui. The GUI is launched by calling linguistica.gui.main() in linguistica/
  • All GUI code is accessible through only linguistica.gui.main() defined in linguistica/gui/ This is important, because PyQt5 may potentially be unavailable at the user’s system. The safeguards against import errors, but other .py files in linguistica/gui do not. Relatedly, when linguistica.gui.main() is to be called (as in linguistica/, there is always code that checks whether PyQt5 is importable before linguistica.gui.main() can actually be called.

Notes on the command line interface (CLI):

  • The CLI code is in linguistica/, all wrapped in linguistica.cli.main() which is called in linguistica/
  • We don’t output words_to_contexts and contexts_to_words, because they are huge… Or we could just output those whose counts are higher than some threshold?


The core dependencies are specified in requirements.txt which is read by and used in build tests by Travis CI. For reproducibility, we pin down each dependency’s major and minor version numbers, while allowing flexibility for getting bug fixes. For example, six>=1.10.0,<=1.10.99 points to the latest six v1.10.x.

There is also dev-requirements.txt with dependencies for running tests and code quality checks. Travis CI uses this file for build tests. It is recommended that developers and administrators of the Linguistica 5 also install these dependencies and use them for maintaining high code quality.


We use pytest as the testing framework. Developers and administrators should install the dependencies for running tests: $ pip install -r dev-requirements

Run tests as often as you can. In particular, it must be run before and after each coding session: $ pytest -vv --cov linguistica linguistica. -vv outputs a verbose test report. --cov linguistica means that we check test coverage for .py files under the directory linguistica (so just the library code). Lastly, the second linguistica in the command specifies the directory (again, the library code) where pytest should look for tests in test_*.py. .coveragerc configures the test coverage report.

We are also using flake8 for maintaining high code quality. Essentially, no PEP8 violations are allowed – not even trailing whitespace or extra empty lines. Run flake8 with $ flake8 linguistica. If you see no terminal output, it means everything is compliant. Note that the Travis CI build tests also run flake8. Do not try to work around the robots!

Continuous integration

The Linguistica 5 repository is set up with Travis CI for automatically running build tests for all pull requests. The configuration is in .travis.yml. We take advantage of continuous integration to:

  • test whether the Linguistica 5 library can be successfully installed
  • check if all tests pass
  • ensure that the codebase is compliant with PEP 8 coding style conventions

Build tests are run for all supported Python versions (2.7 and 3.4+). installs the Linguistica 5 library. It also specifies the metadata of the library (displayed on the PyPI site). Developers and administrators are recommended to install Linguisitca 5 with $ python develop for development purposes.


The readme, README.rst, is in reStructuredText instead of Markdown, simply because PyPI does not seem to render Markdown mark-up for the long_description in contains notes for the administrators of the Linguistica 5 project.


The version number is specified in the text file linguistica/VERSION and nowhere else. The version number in both and linguistica.__version__ points to this text file. It is important to not hard-code or even mention the current version number anywhere else (not even in the source .rst of this documentation) to avoid confusion.

We essentially follow for the major.minor.patch format. The major version is 5 because there’s John’s Linguistica 3 & 4 written in C++. The minor version number increments when a new release comes with new features. The patch number increments when a new release comes with changes with no API ramifications such as bug fixes.

The first release of Linguistica 5 was 5.1.0 instead of 5.0.0, because 5.0.0 was John’s in-house version written in Python 2.


We use Sphinx as the documentation framework, as it is the official tool for Python projects (including the docs of the Python language itself). The source files (in the reStructuredText mark-up language) are in docs/sources/. These source files are what generates the docs/*.html files, which GitHub renders as the documentation website (= what you are reading now). To update the HTML files after the source .rst files are updated, run $ sh

Changes (new features, bug fixes) together with new version releases should be documented in