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rticonnextdds-connector: Python

RTI Connector for Connext DDS

RTI Connector for Connext DDS is a quick and easy way to access the power and functionality of RTI Connext DDS. It is based on XML Application Creation and Dynamic Data.

Language Support

This repository is specific to Python, for other languages (python, lua, C) refer to the main repository of connector.

We use ctypes to call our native functions; everything is hidden in a nice Python wrapper. We tested our Python implementation with both Python 2.7.14 and Python 3.6.3.

Platform support

We are building our library for a few architectures only. Check them out here. If you need another architecture, please contact your RTI account manager or sales@rti.com.

If you want to check the version of the libraries, run the following command:

strings librtiddsconnector.dylib | grep BUILD

Threading model

The Connector Native API does not yet implement any mechanism for thread safety. For now, the responsibility of protecting calls to the Connector is left to you. (In the future we may add thread safety in the native layer.) In Python, you will have to protect the calls to the Connector if you are using different threads. For an example, see Protecting calls to the Connector library.

Support

This is an experimental RTI product. As such, we offer support through the RTI Community forum.

Getting started with Python

Be sure you have Python. Then use pip to install the Connector:

$ pip install rticonnextdds_connector

You can also clone the repository:

$ git clone --recursive https://github.com/rticommunity/rticonnextdds-connector-py.git

Available examples

You can find several sets of examples in this directory: examples/python

  • simple: shows how to write samples and how to read/take.
  • mixed: various examples

Protecting calls to the Connector library

As we explained above, you are responsible for protecting calls to Connector. There are many options in Python to do so; one is to use the threading package:

...
...
import threading
sem = threading.Semaphore();
...
...
#acquire the semaphore
sem.acquire(True);
#call to connector APissem.acquire(True);
input.take();
numOfSamples = input.samples.getLength();
...
...
#release the semaphore
sem.release();
...
...

For more information on the threading Python packages, see the Python documentation here.

API overview

require the Connector library

If you want to use the rticonnextdds_connector, you have to import it:

import rticonnextdds_connector as rti

instantiate a new Connector

To create a new Connector you have to pass an XML file and a configuration name. For more information on the XML format, see the XML App Creation guide or have a look at the ShapeExample.xml file included in this examples directory.

connector = rti.Connector("MyParticipantLibrary::Zero","./ShapeExample.xml");

delete a Connector

To destroy all the DDS entities that belong to a Connector previously created, call the delete function.

connector = rti.Connector("MyParticipantLibrary::Zero","./ShapeExample.xml");
...
...
connector.delete();

write a sample

To write a sample, first get a reference to the output port:

output = connector.getOutput("MyPublisher::MySquareWriter")

Then set the instance's fields:

output.instance.setNumber("x", 1);
output.instance.setNumber("y", 2);
output.instance.setNumber("shapesize", 30);
output.instance.setString("color", "BLUE");

Then write:

output.write();

set the instance's fields:

The content of an instance can be set by using a dictionary that matches the original type, or field by field.

  • Using a dictionary:
#assuming that sample is a dictionary containing
#an object of the same type of the output.instance:

output.instance.setDictionary(sample);
  • Field by field:
output.instance.setNumber("y", 2);

The APIs to set an instance field by field are three: setNumber(fieldName, number); setBoolean(fieldName, boolean); and setString(fieldName, string);.

Nested fields can be accessed with the dot notation: "x.y.z". Arrays or sequences can be accessed with square brakets: "x.y[1].z". For more information on how to access fields, see Section 6.4 Data Access API of the RTI Prototyper Getting Started Guide.

read/take data

To read/take samples, first get a reference to the input port:

input = connector.getInput("MySubscriber::MySquareReader");

Then call the read() or take() API:

input.read();

or

 input.take();

The read/take operation can return multiple samples. So, we have to iterate on an array:

    input.take();
    numOfSamples = input.samples.getLength();
    for j in range (1, numOfSamples+1):
        if input.infos.isValid(j):
            x = input.samples.getNumber(j, "x");
            y = input.samples.getNumber(j, "y");
            size = input.samples.getNumber(j, "shapesize");
            color = input.samples.getString(j, "color");
            toPrint = "Received x: " + repr(x) + " y: " + repr(y) + " size: " + repr(size) + " color: " + repr(color);
            print(toPrint);
}

access sample fields after a read/take

A read() or take() operation can return multiple samples. They are stored in an array. Every time you try to access a specific sample, you have to specify an index (j in the example below).

You can access the data by getting a copy in a dictionary object, or you can access each field individually:

  • Using a dictionary:
 numOfSamples = input.samples.getLength();
 for j in range (1, numOfSamples+1):
     if input.infos.isValid(j):
         sample = input.samples.getDictionary(j);
         #print the whole sample
         print(sample);
         #or print a single element
         print(sample['x']);
 }
  • Field by field:
 numOfSamples = input.samples.getLength();
 for j in range (1, numOfSamples+1):
     if input.infos.isValid(j):
         x = input.samples.getNumber(j, "x");
         y = input.samples.getNumber(j, "y");
         size = input.samples.getNumber(j, "shapesize");
         color = input.samples.getString(j, "color");
         toPrint = "Received x: " + repr(x) + " y: " + repr(y) + " size: " + repr(size) + " color: " + repr(color);
         print(toPrint);
 }

The APIs to access each field individually are three: getNumber(indexm fieldName); getBoolean(index, fieldName); and getString(index, fieldName);.

License

With the sole exception of the contents of the "examples" subdirectory, all use of this product is subject to the RTI Software License Agreement included at the top level of this repository. Files within the "examples" subdirectory are licensed as marked within the file.

This software is an experimental ("pre-production") product. The Software is provided "as is," with no warranty of any type, including any warranty for fitness for any purpose. RTI is under no obligation to maintain or support the software. RTI shall not be liable for any incidental or consequential damages arising out of the use or inability to use the software.