The NWB-N format was designed to be easily extendable. Here we will demonstrate how to extend NWB using the PyNWB API.

Defining extensions

Extensions should be defined separately from the code that uses the extensions. This design decision is based on the assumption that extension will be written once, and read or used multiple times. Here, we provide an example of how to create an extension for subsequent use. (For more information on the available tools for creating extensions, see Extending NWB).

The following block of code demonstrates how to create a new namespace, and then add a new neurodata_type to this namespace. Finally, it calls export to save the extensions to disk for downstream use.

from pynwb import NWBNamespaceBuilder, NWBGroupSpec, NWBAttributeSpec

ns_path = "mylab.namespace.yaml"
ext_source = "mylab.extensions.yaml"

ns_builder = NWBNamespaceBuilder('Extension for use in my Lab', "mylab")
ext = NWBGroupSpec('A custom ElectricalSeries for my lab',
                   attributes=[NWBAttributeSpec('trode_id', 'int', 'the tetrode id')],

ns_builder.add_spec(ext_source, ext)

Running this block will produce two YAML files.

The first file contains the specification of the namespace.

# mylab.namespace.yaml
- doc: Extension for use in my Lab
  name: mylab
  - namespace: core
  - source: fake_extension.yaml

The second file contains the details on newly defined types.

# mylab.extensions.yaml
- attributes:
  - doc: the tetrode id
    dtype: int
    name: trode_id
  doc: A custom ElectricalSeries for my lab
  neurodata_type_def: TetrodeSeries
  neurodata_type_inc: ElectricalSeries

Using extensions

After an extension has been created, it can be used by downstream codes for reading and writing data. There are two main mechanisms for reading and writing extension data with PyNWB. The first involves defining new NWBContainer classes that are then mapped to the neurodata types in the extension.

from pynwb import register_class, load_namespaces
from pynwb.ecephys import ElectricalSeries

ns_path = "mylab.namespace.yaml"

@register_class('mylab', 'TetrodeSeries')
class TetrodeSeries(ElectricalSeries):
    __nwbfields__ = ('tetrode_id',)

    def __init__(self, ...):


Although it is not used here, it is encouraged to use the docval decorator for documenting constructors, methods, and functions.

When extending NWBContainer or NWBContainer subclasses, you should defining the class field __nwbfields__. This will tell PyNWB the properties of the NWBContainer extension.

If you do not want to write additional code to read your extensions, PyNWB is able to dynamically create an NWBContainer subclass for use within the PyNWB API. Dynamically created classes can be inspected using the built-in help or the inspect module.

from pynwb import get_class, load_namespaces

ns_path = "mylab.namespace.yaml"

TetrodeSeries = get_class('TetrodeSeries', 'mylab')


When defining your own NWBContainer, the subclass name does not need to be the same as the extension type name. However, it is encouraged to keep class and extension names the same for the purposes of readibility.


The following are example Jupyter notebooks for converting custom lab data to NWB:

crcns-ret-1: Meister lab retina data