:orphan:

|rss_image|  **2019-03 - 1/1** :ref:`Blog <ap-main-0>` :ref:`machine_learning (5) <ap-cat-machine_learning-0>`

.. |rss_image| image:: feed-icon-16x16.png
    :target: ../_downloads/rss.xml
    :alt: RSS

----


.. index:: 2019-03


.. _ap-month-2019-03-0:

2019-03 - 1/1
+++++++++++++

.. blogpostagg::
    :title: Nogil, numpy, cython
    :date: 2019-03-25
    :keywords: nogil,numpy,blas,lapack
    :categories: cython
    :rawfile: 2019/2019-03-25_nogil.rst

    I had to implement a custom criterion to optimize
    a decision tree and I wanted to leverage :epkg:`scikit-learn`
    instead of rewriting my own. Version 0.21 of :epkg:`scikit-learn`
    introduced some changed in the API which make possible
    to overload an existing criterion and replace some of the logic
    by another one: `_criterion.pyx
    <https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/tree/_criterion.pyx>`_.
    The purpose was to show that a fast implementation requires
    some tricks (see :ref:`piecewiselinearregressioncriterionrst`) and
    `piecewise_tree_regression_criterion.pyx
    <https://github.com/sdpython/mlinsights/blob/master/mlinsights/mlmodel/piecewise_tree_regression_criterion.pyx>`_,
    `piecewise_tree_regression_criterion_fast.pyx
    <https://github.com/sdpython/mlinsights/blob/master/mlinsights/mlmodel/piecewise_tree_regression_criterion_fast.pyx>`_
    for the code. Other than that, every function to overlaod is marked as
    :epkg:`nogil`. Every function or method marked as *nogil* cannot
    go through the :epkg:`GIL` (see also :epkg:`PEP-0311`),
    which no :epkg:`python` object can be created in that method.
    In fact, no :epkg:`python` can be called inside a :epkg:`Cython`
    method protected with *nogil*. The issue with that is that
    any :epkg:`numpy` method cannot be called.
    

    ...





----

|rss_image|  **2019-03 - 1/1** :ref:`2018-05 (1) <ap-month-2018-05-0>` :ref:`2019-02 (4) <ap-month-2019-02-0>` :ref:`2019-03 (1) <ap-month-2019-03-0>` :ref:`2020-09 (1) <ap-month-2020-09-0>` :ref:`2021-01 (1) <ap-month-2021-01-0>`