Client Configuration#

Howso Engine’s python client (HowsoDirectClient) is designed to work well without any special configuration. However, there may be circumstances where additional options may be useful.

How to Create a Configuration File#

The configuration file is a simple YAML text file with the name howso.yml and is located in one of these places:

  1. At any valid file path that is stored in an environment variable: HOWSO_CONFIG,

  2. Within your current working directory,

  3. Within your OS-specific “home” directory inside a directory called .howso,

  • On Windows, the “home” directory is stored in the %USERPROFILE% environment variable.

  • On MacOS or Linux, the “home” directory is the location stored in the $USER environment variable.

  1. Within your configured XDG_DIR_CONFIG_PATH path (see documentation at for more information).


If there are multiple howso.yml files, they will be searched for in the above order and the first one found will be used.

Structure of the configuration file#

The top-level of the file is the howso section:

  • howso

    This is the top-level for Howso Engine options. It has two primary sub-sections: client and client_extra_params:

    • client

      Set the client to use by it’s dotted Python path. The default value is

      This is an advanced user option can be used to define and use other clients which subclass HowsoDirectClient but provide alternate behavior. This may be useful for adding additional authentication, for example.

    • client_extra_params

      This section is for providing options to Amalgam (amalgam) and the Howso Engine (core):

      • amalgam

        Howso Engine is built upon Amalgam. This section holds options that are specific to the usage of Amalgam and/or the Python client: amalgam-lang. The options here are as follows:

        • debug

          • false (the default)

          • true Use this option for additional debugging information in the Amalgam trace files.

        • library_path

          Set a full path to an Amalgam shared library (DLL, SO, DyLib). This is an advanced setting for developers who compile their own Amalgam shared object binaries.

        • arch

          Target CPU architecture of the amalgam library. This is determined programmatically by default and should only be overridden here by advanced users.

          Valid values are:

          • x86_64 - Most Windows, older MacOS, and linux machines

          • arm64 - Modern MacOS and some Linux machines

          • arm64_8a - Specifically compiled for CPUs compatible with generation 1 aarch64 instruction sets such as early Raspberry Pi’s and some early Graviton processors.

        • execution_trace_dir

          Set the desired path where tracefiles should be written. The path must be a valid directory with write permission for the operating user. The default value is the current working directory.

        • execution_trace_file

          Set the desired file name for the trace files. Default value is <trainee_name>.trace.

        • library_postfix

          The Amalgam shared libraries are compiled for different modes of operation. Each of the valid values for this option are:

          • -mt for Multithreaded operation. This is almost always the best option (and is thus the default on most systems).

          • -st for Singlethreaded operation. In rare cases usually involving small Trainee models, this may be the best option.

          • -openmp for Multi Processing using the OpenMP library. This option may be useful when latency is paramount.

          • -pgc for “Pedantic Garbage Collection”. This is exclusively used by developers in Amalgam debugging scenarios.

        • os

          Target operating system of the amalgam library. Valid values are:

          • linux

          • darwin

          • windows

        • trace

          • false (default) - No trace files are written.

          • true - Use this option to generate tracefiles.

      • core

        This section is for changing the behavior of the Howso Engine (the Amalgam shared objects).

        • persisted_trainees_dir

          By default, persisted trainees are stored in the current working directory. Set this option to a valid path with sufficient write permissions to store all persisted trainees if so desired.

        • howso_path

          Sets the location to look for the Howso Engine (core). This is an advanced setting used by developers.

        • howso_fname

          Sets the filename for the Howso Engine (core). This is an advanced setting used by developers.

        • trainee_template_path

          Sets the path to look for the howso-template howso-template. This is an advanced setting used by developers.

Example Configuration File#


By default, the Howso Engine will automatically choose sensible default values making a configuration file entirely optional.

This is an example howso.yml file which overrides a few options for an early model Raspberry Pi

            arch: arm64_8a
            library_postfix: -st
        persisted_trainees_dir: /home/jsmith/howso_trainees