Using NetworkTables

NetworkTables is a communications protocol used in FIRST Robotics. It provides a simple to use mechanism for communicating information between several computers. There is a single server (typically your robot) and zero or more clients. These clients can be on the driver station, a coprocessor, or anything else on the robot’s local control network.

Robot Configuration

Note

These notes apply to all languages that use NetworkTables, not just Python

FIRST introduced the mDNS based addressing for the RoboRIO in 2015, and generally teams that use additional devices have found that while it works at home and sometimes in the pits, it tends to not work correctly on the field at events. For this reason, if you use pynetworktables on the field, we strongly encourage teams to ensure every device has a static IP address.

  • Static IPs are 10.XX.XX.2

  • mDNS Hostnames are roborio-XXXX-frc.local (don’t use these!)

For example, if your team number was 1234, then the static IP to connect to would be 10.12.34.2.

For information on configuring your RoboRIO and other devices to use static IPs, see the WPILib screensteps documentation.

Server initialization (Robot)

WPILib automatically starts NetworkTables for you, and no additional configuration should need to be done.

Client initialization (Driver Station/Coprocessor)

Note

For install instructions, see pynetworktables installation instructions

As of 2017, this is very easy to do. Here’s the code:

from networktables import NetworkTables

NetworkTables.initialize(server='10.xx.xx.2')

The key is specifying the correct server hostname. See the above section on robot configuration for this.

Warning

NetworkTables does not connect instantly! If you write a script that calls initialize and immediately tries to read from NetworkTables, you will almost certainly not be able to read any data.

To write a script that waits for the connection, you can use the following code:

import threading
from networktables import NetworkTables

cond = threading.Condition()
notified = [False]

def connectionListener(connected, info):
    print(info, '; Connected=%s' % connected)
    with cond:
        notified[0] = True
        cond.notify()

NetworkTables.initialize(server='10.xx.xx.2')
NetworkTables.addConnectionListener(connectionListener, immediateNotify=True)

with cond:
    print("Waiting")
    if not notified[0]:
        cond.wait()

# Insert your processing code here
print("Connected!")

Theory of operation

In its most abstract form, NetworkTables can be thought of as a dictionary that is shared across multiple computers across the network. As you change the value of a table on one computer, the value is transmitted to the other side and can be retrieved there.

The keys of this dictionary must be strings, but the values can be numbers, strings, booleans, various array types, or raw binary. Strictly speaking, the keys can be any string value, but they are typically path-like values such as /SmartDashboard/foo.

When you call NetworkTables.getTable, this retrieves a NetworkTable instance that allows you to perform operations on a specified path:

table = NetworkTables.getTable('SmartDashboard')

# This retrieves a boolean at /SmartDashboard/foo
foo = table.getBoolean('foo', True)

There is also an concept of subtables:

subtable = table.getSubTable('bar')

# This retrieves /SmartDashboard/bar/baz
baz = table.getNumber('baz', 1)

As you may have guessed from the above example, once you obtain a NetworkTable instance, there are very simple functions you can call to send and receive NetworkTables data.

  • To retrieve values, call table.getXXX(name, default)

  • To send values, call table.putXXX(name, value)

NetworkTables can also be told to call a function when a particular key in the table is updated.

Code Samples

There are many code samples showing various aspects of NetworkTables operation. See the pynetworktables examples page.

See also

NetworkTables API Reference

Troubleshooting

See also

pynetworktables troubleshooting

External tools

WPILib’s OutlineViewer (requires Java) is a great tool for connecting to networktables and seeing what’s being transmitted.

WPILib’s Shuffleboard (requires Java) is the new (as of 2018) tool to replace SmartDashboard for creating custom NetworkTables-enabled dashboards.

WPILib’s SmartDashboard (requires Java) is an older tool used by teams to connect to NetworkTables and used as a dashboard.