Developer Documentation

Design principle

pysptk is a thin python wrapper of SPTK. It is designed to be API consistent with the original SPTK as possible, but give better interface. There are a few design principles to wrap C interface:

  1. Avoid really short names for variables (e.g. a, b, c, aa, bb, dd)

    Variable names should be informative. If the C functions have such short names, use self-descriptive names instead for python interfaces, unless they have clear meanings in their context.

  2. Avoid too many function arguments

    Less is better. If the C functions have too many function arguments, use keyword arguments with proper default values for optional ones in python.

  3. Handle errors in python

    Since C functions might exit (unfortunately) inside their functions for unexpected inputs, it should be check if the inputs are supported or not in python.

To wrap C interface, Cython is totally used.

How to build pysptk

You have to install numpy and cython first, and then:

git clone
cd pysptk
git submodule update --init
python develop

should work.


Dependency to the SPTK is added as a submodule. You have to checkout the supported SPTK as git sudmobule update --init before running

How to build docs

pysptk docs are managed by the python sphinx. Docs-related dependencies can be resolved by:

pip install .[docs]

at the top of pysptk directory.

To build docs, go to the docs directory and then:

make html

You will see the generated docs in _build directory as follows (might different depends on sphinx version):

% tree _build/ -d
├── doctrees
│   └── generated
├── html
│   ├── _images
│   ├── _modules
│   │   └── pysptk
│   ├── _sources
│   │   └── generated
│   ├── _static
│   │   ├── css
│   │   ├── fonts
│   │   └── js
│   └── generated
└── plot_directive
    └── generated

See _build/html/index.html for the top page of the generated docs.

How to add a new function

There are a lot of functions unexposed from SPTK. To add a new function to pysptk, there are a few typical steps:

  1. Add function signature to _sptk.pxd
  2. Add cython implementation to _sptk.pyx
  3. Add python interface (with docstrings) to (or some proper module)

As you can see in, _sptk.pyx and SPTK sources are compiled into a single extension module.


You might wonder why cython implementation and python interface should be separated because cython module can be directly accessed by python. The reasons are 1) to avoid rebuilding cython module when docs strings are changed in the source 2) to make doc looks great, since sphinx seems unable to collect function argments correctly from cython module for now. Relevant issue: pysptk/#33

An example

In _sptk.pyd:

cdef extern from "SPTK.h":
    double _agexp "agexp"(double r, double x, double y)

In _sptk.pyx:

def agexp(r, x, y):
    return _agexp(r, x, y)

In sptk.pyx:

def agexp(r, x, y):
    """Magnitude squared generalized exponential function

    r : float
    x : float
        Real part
    y : float
        Imaginary part


    return _sptk.agexp(r, x, y)