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.. _upgrade:
Upgrading From Pre-3.0 Versions
===============================
The version 3 release of emcee is the biggest update in years.
That being said, we've made every attempt to maintain backwards compatibility
while still offering new features.
The main new features include:
1. A :ref:`moves-user` interface that allows the use of a variety of ensemble
proposals,
2. A more self consistent and user-friendly :ref:`blobs` interface,
3. A :ref:`backends` interface that simplifies the process of serializing the
sampling results, and
4. The long requested progress bar (implemented using `tqdm
<https://github.com/tqdm/tqdm>`_) so that users can watch the grass grow
while the sampler does its thing (this is as simple as installing tqdm and
setting ``progress=True`` in :class:`EnsembleSampler`).
To improve the stability and supportability of emcee, we also removed some
features.
The main removals are as follows:
1. The ``threads`` keyword argument has been removed in favor of the ``pool``
interface (see the :ref:`parallel` tutorial for more information).
The old interface had issues with memory consumption and hanging processes
when the sampler object wasn't explicitly deleted.
The ``pool`` interface has been supported since the first release of emcee
and existing code should be easy to update following the :ref:`parallel`
tutorial.
2. The ``MPIPool`` has been removed and forked to the `schwimmbad
<https://github.com/adrn/schwimmbad>`_ project.
There was a longstanding issue with memory leaks and random crashes of the
emcee implementation of the ``MPIPool`` that have been fixed in schwimmbad.
schwimmbad also supports several other ``pool`` interfaces that can be used
for parallel sampling.
See the :ref:`parallel` tutorial for more details.
3. The ``PTSampler`` has been removed and forked to the `ptemcee
<https://github.com/willvousden/ptemcee>`_ project.
The existing implementation had been gathering dust and there aren't enough
resources to maintain the sampler within the emcee project.
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