Creating a custom data type

The data types that are available in Sympathy include Table, ADAF, Text, and lists of these types, but if the need should arise you can also make your own data type.

Please keep in mind that this is an advanced operation that is not needed for most users. Furthermore:

  • Nodes can only be connected to other nodes that use the same data type. So a node using your own data type can only be connected to other nodes that use your own data type.
  • Do not duplicate functionality for several different data types. For example Select rows operation should probably only exist for Table.
  • Create paths to and from Table or some other native data type so people using your nodes can still benefit from the standard library and any third party libraries using the standard data types. See Working with ADAF for an example.

By following this guide, you should be able to create a new composite data type out of the existing fundamental data types in sympathy. An example of such a data type is the ADAF. Even many types of data which are not most naturally represented as a hierarchical collection of tables can be created in this fashion. For example an array type could be created by using a single table and building a specialized and more restrictive typeutil interface. Even the ubiquitous Table can be said to be a composite data type as it is a wrapper around the more fundamental sytable type.

Create typeutils class

Creating a new type, requires subclassing sympathy.api.typeutil.TypeAlias and wrapping the class in the sympathy.api.typeutil.typeutil decorator.

The TypeAlias class has the following API:

class sympathy.api.typeutil.TypeAlias(fileobj=None, data=None, filename=None, mode='r', scheme='hdf5', source=None, managed=False, import_links=False)[source]

Return new TypeAlias that does not share references with self. Must be re-implemented by subclasses that define their own storage fields.

classmethod icon()[source]

Return full path to svg icon.


Perform any initialization, such as, defining local fields.

names(kind=None, **kwargs)[source]

Return relevant names. Useful if this type has some kind of names that would be useful in adjust_parameters.

source(other, shallow=False)[source]

Update self with the data from other, without keeping the old state. When shallow is False (default), self should be updated with a deepcopy of other.

self and other must be of the exact same type.


Synchronize data fields that are kept in memory against self._data.

Called before data is written to disk and must be re-implemented by subclasses that define custom storage fields.

classmethod viewer()[source]

Return viewer class, which must be a subclass of sympathy.api.typeutil.ViewerBase

This is the only mandatory step towards creating your own data type. Create a new Python file anywhere in the package inside the Common folder of your library. Name it as your data type, all lower case. In our example we will place the file at boblib/Common/boblib/ Open your new file and add a TypeAlias subclass called File wrapped in the typeutil decorator. Use the method init to do any initialization.

import os
from sympathy.api import typeutil
# Full path to the directory where this file is located.
_directory = os.path.abspath(os.path.dirname(__file__))

@typeutil.typeutil('sytypealias twin_tables = (first: table, second: table)')
class File(typeutil.TypeAlias):
    """Twin tables."""

    def init(self):
        self.first = self._data.first
        self.second = self._data.second

    def viewer(cls):
        from . import twin_tables_viewer
        return twin_tables_viewer.TwinTablesViewer

    def icon(cls):
        return os.path.join(_directory, 'port_twin_tables.svg')

The argument to the decorator is the declaration of your data type. It can contain a combination of basic data types (such as sytable or sytext) other composite types (such as adaf or table), and container types (sylist, sydict, and syrecord).

Create a list of elements by surrounding the name of a type in brackets. For example [adaf].
Create a dictionary of elements by surrounding the name of a type in curly braces. For example {sytable}.
A record contains a few fixed elements. Create a record by surrounding key-value pairs with parenthesis. For example (projects: sytable, coffee_budget: sytable). The values must all be valid types and the keys must all be valid python identifiers. As seen in the example above the elements are available as attributes of the record.

The instance variable self._data will contain the declared data structure. Where applicable, stuff in self._data will be wrapped in the correct typeutil class. In the above example the tables will be wrapped in the typeutils class typeutils.table.File, but if the declared type had been '(first: sytable, second: sytable)', the tables would be bare types.sytable objects and not wrapped in the typeutils class.

The typeutil class should contain any interface to the data that you want to expose to nodes working with this data type. In our example the interface is simply two instance variables called first and second, but for example the typeutils class for the table type defines many methods for reading and writing data and the ADAF typeutil even defines several additional classes.

Locate port type

In order for the type to be fully usable, Sympathy needs to be able to locate it. It is located using a function called library_types() that should be present in the file of your package under Common.

Example from the standard library:

# Filename Library/Common/sylib/

import sympathy.api

def library_types():
    return [

For TwinTables it would look something like:

# Filename boblib/Common/boblib/

from . import twin_tables

def library_types():
    return [twin_tables.File]

Create port type

This step is not strictly necessary but will make it easier to create nodes that use your data type. Add a new port type function to the same file as your typeutils class. It should be similar to the static methods of the Port class of utils.port.


from sympathy.utils import port

def TwinTables(description, name=None):
    return port.CustomPort('twin_tables', description, name=name)

Create an example node

Create a node that uses the new port type:

import numpy as np

from sympathy.api import node as synode
from sympathy.api.nodeconfig import Ports

from boblib.twin_tables import TwinTables

class TwinTablesExample(synode.Node):
    Outputs a twin table with one column in the first table with values 1-99.
    name = 'Twin tables example'
    description = 'Outputs a twin table with one column in first table with values 1-99.'
    icon = 'example.svg'

    nodeid = 'org.sysess.sympathy.examples.twintablesexample'
    author = 'Magnus Sanden <>'
    copyright = '(c) 2014 System Engineering Software Society'
    version = '1.0'

    outputs = Ports([TwinTables('Output', name='port1')])

    def execute(self, node_context):
        """Execute node"""
        tablefile = node_context.output['port1'].first
        data = np.arange(1, 101, dtype=int)
        tablefile.set_name('Output Example')
        tablefile.set_column_from_array('Enumeration', data)

Look at the data on the out port by right-clicking on it and choosing Copy File Path To Clipboard and pasting the path into HDF5View.

Adding an icon

To customize your new type by adding an icon, first create an svg icon for TwinTables. See the icons in Sympathy/Gui/Resources/icons/ports for more details about what the platform icons look like.

Icons should have a width and height of 16. Use an existing platform icon as a template if you are uncertain. If this criteria is not met, the icon will be scaled and cropped to a width and height of 16 automatically.

Once the icon is created, copy it to boblib/Common/boblib/port_twin_tables.svg. The free software Inkscape can be used to create the icons.

Extend the data viewer

To be able to view the data on ports of type twin_tables, a new viewer needs to be created.

Add a module called to boblib/Common/boblib/ with the following code:

from sympathy.api import table
from sympathy.api import qt2
from sympathy.api.typeutil import ViewerBase

class TwinTablesViewer(ViewerBase):
    def __init__(self, data=None, console=None, parent=None):
        super(TwinTablesViewer, self).__init__(parent)

        TableViewer = table.File.viewer()
        self._table1_viewer = TableViewer()
        self._table2_viewer = TableViewer()

        layout = qt2.QtWidgets.QVBoxLayout()


    def data(self):
        return self._data

    def update_data(self, data):
        self._data = data
        if data is not None: