PyLECO

Python reference implementation of the Laboratory Experiment COntrol (LECO) protocol.

The reviewed branch contains reviewed code, which does not yet contain all necessary modules and classes. Development happens in the main branch.

Note: LECO is still under development, such that the code and API might change. The LECO protocol branch pyleco-state contains the assumptions used in this project, which are not yet accepted into the LECO main branch. These things might change, if LECO defines them differently.

For a tutorial on how to get started, see GETTING_STARTED.md.

Quick Start

1. Install Python,
2. Execute pip install pyleco,
3. Import pyleco in your python scripts.

LECO Overview

Network Topology

PyLECO is an implementation of LECO, for the full protocol specifications please visit https://github.com/pymeasure/leco-protocol. LECO offers a protocol for data exchange, for example for laboratory experimental control.

There exist two different communication protocols in LECO.

1. The control protocol allows to exchange messages between any two Components in a LECO network, which is useful for controlling devices.
2. The data protocol is a broadcasting protocol to send information to all those, who want to receive it, which is useful for regular measurement data or for log entries.

A LECO network needs at least one Coordinator (server), which routes the messages among the connected Components.

Each Component has a name unique in the network. This name consists in the name of the Coordinator they are connected to and their own name. For example N1.component1 is the full name of component1 connected to the Coordinator of the Namespace N1. The Coordinator istelf is always called COORDINATOR.

Remote Procedure Calls

The default messaging content of the control protocol are remote procedure calls (RPC) according to jsonrpc. With these RPCs you execute a method on the remote Component. For example you have an Actor, which is for example a Component controlling a measurement instrument. In order to set the output of that measurement instrument, you want to call the set_output method of that instrument. For that purpose, you send a message which encodes exactly that (via jsonrpc): the method to call and the parameters of that method.

Usage of the Control Protocol

Minimum Setup

For a minimum setup, you need:

• a Coordinator (just execute coordinator in your terminal or run the coordinator.py file with your Python interpreter)
• one Component

For example, you can use a Communicator instance to send/receive messages via LECO protocol. The following example requests the list of Components connected to the Coordinator:

from pyleco.utils.communicator import Communicator

c = Communicator(name="TestCommunicator")
connected_components = c.ask_rpc(method="send_local_components")
print(connected_components)

Instrument Control

Let's say you have an instrument with a pymeasure driver Driver, which you want to control.

You need to start (in different threads):

• a Coordinator (as shown above).
• an Actor instance listening to commands and controlling the instrument: actor = Actor(name="inst_actor", cls=Driver). For an example see the pymeasure_actor.py in the examples folder.
• a TransparentDirector: director=TransparentDirector(actor="inst_actor"). The actor parameter has to match the Actor's name parameter. For an example of a measurement script see measurement_script.py in the examples folder.

If you want to set some property of the instrument (e.g. instrument.voltage = 5), you can just use the director transparently: director.device.voltage = 5. In the background, the TransparentDirector, which does not have a device, sends a message to the Actor to set that parameter. The Actor in turn sets that parameter of the instrument driver, which in turn will send some command to the device to take an appropriate action (e.g. setting the voltage to 5 V).

Currently you cannot call methods in a similar, transparent way, without manual intervention. You can add RemoteCall descriptor (in transparent_director module) to the director for each method call you want to use. Afterwards you can use these methods transparently similar to the property shown above.

Overview of Offered Packages and Modules

See the docstrings of the individual classes for more information and for examples.

• The core subpackage contains elements necessary for implementing LECO, especially the Message class, which helps to create and interpret LECO messages.
• The utils subpackage contains modules useful for creating LECO Components.
  • TheCommunicator can send and receive messages, but neither blocks (just for a short time waiting for an answer) nor requires an extra thread. It is useful for usage in scripts.
  • The MessageHandler handles incoming messages in a continuous loop (blocking until stopped). It is useful for creating standalone scripts, like tasks for the Starter.
  • The Listener offers the same interface as the Communicator, but listens in an extra thread for incoming messages. It is useful if you want to react to incoming messages (via data or control protocol) and if you want to send messages of your own accord, for example for GUI applications.
• The coordinators subpackage contains the differenc Coordinators.
  • Coordinator is the Coordinator for the control protocol (exchanging messages).
  • proxy_server is the Coordinator for the data protocol (broadcasting).
• The actors subpackage contains Actor classes to control devices.
• The management subpackage contains Components useful for experiment management
  • The Starter can execute tasks in separate threads. A task could be an Actor controlling some Device.
  • The DataLogger listens to published data (data protocol) and collects them.
• The directors subpackage contains Directors, which facilitate controlling actors or management utilities.
  • For example the CoordinatorDirector has a method for getting Coordinators and Components connected to a Coordinator.
  • The TransparentDirector reads / writes all messages to the remote actor, such that you use the director's device as if it were the instrument itself.

PyLECO extras

The pyleco-extras package contains additional modules. Among them are GUIs controlling the DataLogger and the Starter.