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 Moves interface that allows the use of a variety of ensemble proposals,

  2. A more self consistent and user-friendly Blobs interface,

  3. A Backends interface that simplifies the process of serializing the sampling results, and

  4. The long requested progress bar (implemented using 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 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 Parallelization 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 Parallelization tutorial.

  2. The MPIPool has been removed and forked to the 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 Parallelization tutorial for more details.

  3. The PTSampler has been removed and forked to the ptemcee project. The existing implementation had been gathering dust and there aren’t enough resources to maintain the sampler within the emcee project.