Nushell Plugin Library for Python

Okay, I’ve been going a little nuts with nushell lately, and the reason is because I have a thought process like:

Oh, I want to build this thing!
Maybe there could be a tool to help to build the thing?
Hmm, who is going to make it...
I guess I can do it?

And then I go off and make the tool! In this case, I had tried creating standalone plugins with Python and GoLang, and then I realized that it would be much easier to have a module to help me out. Yesterday I did this for GoLang, so today I figured I’d give Python a shot! And that’s what I’ll briefly show in this post. Note that every feature implemented by the plugins interface isn’t provided here (for example, I still need to add positional arguments and support for pipes into a sink) but this is definitely something to get us started! Check out the module here:

vsoch/nushell-plugin-python

Now let’s go through a few examples. For full examples, you can see the examples folder. Each example includes container builds, a Makefile, a README with instructions, and of course a Python script. When appropriate, there are containers that will help you build a standalone executable.

Filter Plugin

A basic filter plugin will instantiate the FilterPlugin class, and then provide a function to run for the filter. Here is a quick example script.

#!/usr/bin/env python3

from nushell.filter import FilterPlugin

# Your filter function will be called by the FilterPlugin, and should
# accept the plugin and the dictionary of params
def runFilter(plugin, params):
    '''runFilter will be executed by the calling SinkPlugin when method is "sink"
    '''
    # Get the string primitive passed by the user
    value = plugin.get_string_primitive()
    # Calculate the length
    intLength = len(value)
    # Print an integer response (can also be print_string_response)
    plugin.print_int_response(intLength)

# The main function is where you create your plugin and run it.
def main():

    # Initialize a new plugin
    plugin = FilterPlugin(name="len", 
                          usage="Return the length of a string")

    # Run the plugin by passing your filter function
    plugin.run(runFilter)

if __name__ == '__main__':
    main()

Notably, your filter function should taken a plugin and parsed command line parameters (dictionary) as arguments. You can use the plugin to perform several needed functions to send responses back to nushell, or log to /tmp/nushell-plugin-<name>.log: Generally, the functions of interest will be to get or print a string or int response that is passed to or from Nushell.

# basic functions to get / print strings and ints
plugin.get_string_primitive()
plugin.get_int_primitive()
plugin.print_int_response()
plugin.print_string_response()

or to log something to the logfile:

# The logger logs to /tmp/nu_plugin_<name>.log
plugin.logger.info("This is some information")
plugin.logger.debug("The answer is moo.")
plugin.logger.warning("Stinky socks!")
plugin.logger.error("It's all crashed.")

The default level is debug, and you can also disable logging when you create your plugin.

plugin = FilterPlugin(name="len", 
                      usage="Return the length of a string",
                      logging=False)

Sink Plugin

A sink plugin will instantiate the SinkPlugin class, and then hand off stdin (via a temporary file) to a sink function that you write. Here is a dummy example.

#!/usr/bin/env python3

from nushell.sink import SinkPlugin

# Your sink function will be called by the sink Plugin, and should
# accept the plugin and the dictionary of params
def sink(plugin, params):
    '''sink will be executed by the calling SinkPlugin when method is "sink"
    '''
    message = "Hello"
    excited = params.get("excited", False)
    name = params.get("name", "")
    # If we have a name, add to message
    message = "%s %s" %(message, name)
    # Are we excited?
    if excited:
        message += "!"
    print(message)


# The main function is where you create your plugin and run it.
def main():

    # Initialize a new plugin
    plugin = SinkPlugin(name="hello", 
                        usage="A friendly plugin")
    # Add named arguments (notice we check for in params in sink function)
    # add_named_argument(name, argType, syntaxShape=None, usage=None)
    plugin.add_named_argument("excited", "Switch", usage="add an exclamation point!")
    plugin.add_named_argument("name", "Optional", "String", usage="say hello to...")
    # Run the plugin by passing your sink function
    plugin.run(sink)

if __name__ == '__main__':
    main()

Notice that the main difference here is that we are adding named arguments. A switch is basically a boolean, and an Optional (or Mandatory) argument can be a String, Int, or other valid types.

Single Binary

In that you are able to compile your module with pyinstaller you can build your python script as a simple binary, and one that doesn’t even need nushell installed as a Python module anymore. Why might you want to do this? It will mean that your plugin is a single file (binary) and you don’t need to rely on modules elsewhere in the system. I suspect there are other ways to compile python into a single binary (e.g., cython) but this was the first I tried, and fairly straight forward. If you find a different or better way, please contribute to this code base! The examples for len (filter) and hello (sink) demonstrate this, while pokemon didn’t work due to an external data file.

That’s it! I can’t believe I pulled this off in under a day, please contribute to make it better!

Suggested Citation:

Sochat, Vanessa. "Nushell Plugin Library for Python." @vsoch (blog), 24 Oct 2019, https://vsoch.github.io/2019/nushell-plugin-python-module/ (accessed 18 Nov 24).

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