PSyclone reads various run-time configuration options from the psyclone.cfg file. As described in Configuration, the default psyclone.cfg configuration file is installed in <python-base-prefix>/share/psyclone/ during the installation process. The original version of this file is in the PSyclone/config directory of the PSyclone distribution.

At execution-time, the user can specify a custom configuration file to be used. This can either be done with the --config command line option, or by specifying the (full path to the) configuration file to use via the PSYCLONE_CONFIG environment variable. If the specified configuration file is not found then PSyclone will fall back to searching in a list of default locations.

The ordering of these locations depends upon whether PSyclone is being run within a Python virtual environment (such as venv). If no virtual environment is detected then the locations searched, in order, are:

  1. ${PWD}/.psyclone/

  2. ${HOME}/.local/share/psyclone/

  3. <python-base-dir>/share/psyclone/

where <python-base-dir> is the path stored in Python’s sys.prefix.

If a virtual environment is detected then it is assumed that the share directory will be a part of that environment. In order to maintain isolation of distinct virtual environments this directory is then checked before the user’s home directory. i.e. the list of locations searched is now:

  1. ${PWD}/.psyclone/

  2. <python-base-dir>/share/psyclone/

  3. ${HOME}/.local/share/psyclone/

Note that for developers a slightly different configuration handling is implemented, see Module: configuration for details.


The configuration file is read by the Python ConfigParser class ( and must be formatted accordingly. It currently consists of a DEFAULT section e.g.:

DEFAULTAPI = dynamo0.3
PSYIR_ROOT_NAME = psyir_tmp
VALID_PSY_DATA_PREFIXES = profile, extract

and an optional API specific section, for example for the dynamo0.3 section:

access_mapping = gh_read: read, gh_write: write, gh_readwrite: readwrite,
                 gh_inc: inc, gh_readinc: readinc, gh_sum: sum
supported_fortran_datatypes = real, integer, logical
default_kind = real: r_def, integer: i_def, logical: l_def

or for gocean1.0:

access_mapping = go_read:read, go_write:write, go_readwrite:readwrite
grid-properties = go_grid_xstop: {0}%%grid%%subdomain%%internal%%xstop: scalar,
               go_grid_ystop: {0}%%grid%%subdomain%%internal%%ystop: scalar,
               go_grid_data: {0}%%data: array,

The meaning of the various entries is described in the following sub-sections.

Note that ConfigParser supports various forms of boolean entry including “true/false”, “yes/no” and “1/0”. See for more details.


This section contains entries that are, in principle, applicable to all APIs supported by PSyclone.




The API that PSyclone assumes an Algorithm/Kernel conforms to if no API is specified. Must be one of the APIs supported by PSyclone (“dynamo0.3”, “gocean1.0” and “nemo”). If there is no API specified and there is only one API-specific section in the config file loaded, this API will be used. This value can be overwritten by the command line option ‘-api’. If there is no API entry in the config file, and ‘-api’ is not specified on the command line, “dynamo0.3” is used as default.


The API that the kernel-stub generator assumes by default. Must be one of the stub-APIs supported by PSyclone (“dynamo0.3” only at this stage).


Whether or not to generate code for distributed-memory parallelism by default. Note that this is currently only supported for the LFRic (Dynamo 0.3) API.


Whether or not to generate code for reproducible OpenMP reductions (see Reductions) by default.


If generating code for reproducible OpenMP reductions, this setting controls the amount of padding used between elements of the array in which each thread accumulates its local reduction. (This prevents false sharing of cache lines by different threads.)


The root for generated PSyIR symbol names if one is not supplied when creating a symbol. Defaults to “psyir_tmp”.


Which class prefixes are permitted in any PSyData-related transformations. See PSyData API for details.

Common Sections

The following entries must be defined for each API in order for PSyclone to work as expected:




This field defines the strings that are used by a particular API to indicate write, read, … access. Its value is a comma separated list of access-string:access pairs, e.g.:

gh_read: read, gh_write: write, gh_readwrite: readwrite, gh_inc: inc, gh_readinc: gh_sum: sum

At this stage these 6 types are defined for read, write, read+write, increment, read+increment and summation access by PSyclone. Sum is a form of reduction. The GOcean API does not support increment or sum, so it only defines three mappings for read, write, and readwrite.

dynamo0.3 Section

This section contains configuration options that are only applicable when using the LFRic (Dynamo 0.3) API.




Whether or not to perform redundant computation over annexed dofs in order to reduce the number of halo exchanges, see Annexed DoFs.


Captures the supported Fortran data types of LFRic arguments, see Supported Data Types and Default Kind.


Captures the default kinds (precisions) for the supported Fortran data types in LFRic, see Supported Data Types and Default Kind.


Specifies whether to generate run-time validation checks, see Run-time Checks.


Sets the number of ANY_SPACE function spaces in LFRic, see Number of Generalised ANY_*_SPACE Function Spaces.


Sets the number of ANY_DISCONTINUOUS_SPACE function spaces in LFRic, see Number of Generalised ANY_*_SPACE Function Spaces.

gocean1.0 Section

This section contains configuration options that are only applicable when using the Gocean 1.0 API.




This contains definitions of additional iteration spaces used by PSyclone. A detailed description can be found in the Iteration-spaces section of the GOcean1.0 chapter.


This key contains definitions to access various grid properties. A detailed description can be found in the Grid Properties section of the GOcean1.0 chapter.

NEMO Section

This section contains configuration options that are only applicable when using the NEMO API.




This declares a mapping for a certain loop level, specified as TYPE. Each value must have three key:value pairs. A value can be empty if it is not required or not known, but the key must still be specified. The required keys are:

var: the variable name that indicates the loop level,

start: the first loop iteration, and

stop: the last loop iteration.

Each loop detected by the NEMO API will be given one of the TYPE values specified in the configuration file. See the example below for more details.


Specifies the order in which loops are created when converting an implicit loop to an explicit loop. All values in this comma-separated list must have a corresponding mapping-TYPE value defined.

Below we show an example of the NEMO section of a PSyclone configuration file. Note how the values in index-order have corresponding mapping entries, e.g. mapping-lon, mapping-lat etc.:

mapping-lon = var: ji, start: 1, stop: jpi
mapping-lat = var: jj, start: 1, stop: jpj
mapping-levels = var: jk, start: 1, stop: jpk
mapping-tracers = var: jt, start: 1, stop:
mapping-unknown = var: , start: 1, stop:

index-order = lon, lat, levels, tracers

If a NEMO loop then uses Do jj=..., PSyclone will give this loop the type ‘lat’, because the loop uses the variable name specified in the configuration file for a loop of type ‘lat’. The loop type can be accessed using loop.loop_type, i.e. in this example it will be loop.loop_type == 'lat'.

The entry mapping-unknown has an empty value for the key ‘var’. This means that the type ‘unknown’ will be used for any loop that can not be mapped using any of the other variable names in the configuration file.