languages.rst

Supported Languages

NStack is language-agnostic and allows you to write modules in multiple languages and connect them together -- currently we support Python, with R and Java coming soon. More languages will be added over time -- if there's something you really need, please let us know!

Python

Basic Structure

NStack services in Python inherit from a base class, called Module within the nstack module:

import nstack

class Module(nstack.Module):
    def numChars(self, msg):
        return len(msg)

Note

Ensure you import the nstack module in your service, e.g. import nstack

Any function that you export within the API section of your nstack yaml must exist as a method on this class (you can add private methods on this class for internal use as expected in Python).

Data comes into this function via the method arguments - for nstack all the data is passed within a single argument that follows the self parameter. For instance, in the example above there is a single argument msg consisting of a single string element that may be used as-is. However if your function was defined as taking (Double, Double), you would need to unpack the tuple in Python first as follows,

def test(self, msg):
    x, y = msg
    ...

Similarly, to return data from your NStack function, simply return it as a single element within your Python method, as in the top example above.

The NStack object lasts for the life-time of the workflow. Any initialisation can be performed within the object startup method that will be called automatically on service start, e.g. open a database connection, load a data-set, etc. Similarly a shutdown method is called on service shutdown, this provides a short time window, 90s, to perform any required shutdown routines before the service is terminated i.e.

import nstack

class Module(nstack.Module):
    def startup(self):
        # custom initialisation here

    def shutdown(self):
        # custom shutdown here

Notes

• Anything your``print`` will show up in nstack log to aid debugging. (all output on stdout and stderr is sent to the NStack logs)
• Extra libraries from pypi using pip can be installed by adding them to the requirements.txt file in the project directory - they will be installed during nstack build

Mapping NStack types to Python types

The table below show you what python types to expect and to return when dealing with types defined in the NStack IDL as defined in :ref:`nstack_types`:

NStack Type	Python Type
Integer	int
Double	float
Boolean	bool
Text	str
()	() (empty tuple) or None
Tuple	tuple
Struct	dict
Array	list
[Byte]	bytes
x optional	None or x
Json	a json-encoded string *

*Allows you to specify services that either take or receive Json-encoded strings as parameters.

R

Coming soon

Java

Coming soon