nushell 0.0.16

Python module to easily create nushell plugins

Nushell Plugin Python

This is a python module to allow for easy creation of plugins. It's already fairly easy, but this can improve upon that! Each of the examples provided comes with:

• the full example in a python file (without the .py extension)
• containers with nushell to run with regular Python or (for some) a standalone binary (via pyinstaller)
• README.md files to walk through the usage

Quick start examples for a filter and sink plugin are included below, and you should see the examples folder for the complete code, makefiles, and Dockerfiles. Please contribute new examples along with tweaks to the code! I developed this in under a day, so we can likely make it much better, and will need to as nushell is developed.

Install

You can install from pip

$ pip install nushell

or from source here:

$ git clone https://github.com/vsoch/nushell-plugin-python
cd nushell-plugin-python
python setup.py install

Plugin Class Arguments

The following are shared parameters for both filter and sink plugins.

Name	Description	Required or Default
name	the name of the plugin	required
usage	plugin usage	required
logging	enable logging to nu_plugin_<name>.log	defaults to True (enabled)
add_help	add the --help flag	defaults to True
parse_params	extract parameters from items	defaults to True

Parameters

Parameters can be named or positional arguments that are defined for your plugin. You can actually have positional and named arguments with the same name, and define the help string for one (and it will be used by the other).

Named Parameters

For either a sink or a filter, you can pass in named arguments, meaning that your plugin will parse them like:

$ <plugin> --<name> <value>

or for a boolean (called a Switch)

$ <plugin> --<switch>

Here are examples of adding all kinds of named arguments

# add_named_argument(name, argType, syntaxShape=None, usage=None)
plugin.add_named_argument("catch", "Switch", usage="catch a random pokemon")
plugin.add_named_argument("list", "Switch", usage="list pokemon names")
plugin.add_named_argument("list-sorted", "Switch", usage="list sorted names")
plugin.add_named_argument("avatar", "Optional", "String", "generate avatar")
plugin.add_named_argument("pokemon", "Optional", "String", "get pokemon")

For an argument to be Mandatory, just change "Optional" to "Mandatory" (the above plugin doesn't require anything).

Positional Arguments

Positional arguments come after the plugin name, but don't have a flag. For example:

$ <plugin> <positional>

Here are examples of adding positional arguments. Each needs a name, if it's Mandatory or Optional (there is no Switch), the SyntaxShape (e.g. String, Int, Any) and then a usage string.

# add_positional_argument(name, argType, syntaxShape=None, usage=None)
plugin.add_positional_argument("number", "Mandatory", "Int", usage="number to parse")
plugin.add_positional_argument("secondNumber", "Optional", "Any", usage="second number to parse")

Filter Plugin

A basic filter plugin will instantiate the FilterPlugin class, and then provide a function to run for the filter.

#!/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:

plugin.logger.<level>
plugin.get_string_primitive()
plugin.get_int_primitive()
plugin.print_int_response()
plugin.print_string_response()

Examples

• len is a basic function to return the length of a string
• plus adds two ints, and is an example with positional arguments

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()

Parameters

Since you can pipe content into a sink, the piped content is parsed into a list and passed with params as the _pipe key. For example, if we do:

> ls | get name | hello --name Dinosaur
Hello Dinosaur

And then look in the output file, we see that the parsed params include a pipe of all the named of the listed files (that we generated above)

PARAMS {'name': 'Dinosaur', '_pipe': ['Makefile', 'README.md', 'Dockerfile', 'nu_plugin_hello', 'Dockerfile.standalone']}

If you don't want to parse the pipe, set your plugin.parse_pipe to False:

plugin.parse_pipe = False
plugin.run(sink)

And the result will include the full list of entries with items and tags.

PARAMS {'name': 'Dinosaur', '_pipe': [[{'tag': {'anchor': None, 'span': {'start': 0, 'end': 2}}, 'item': {'Primitive': {'String': 'Makefile'}}}, {'tag': {'anchor': None, 'span': {'start': 0, 'end': 2}}, 'item': {'Primitive': {'String': 'README.md'}}}, {'tag': {'anchor': None, 'span': {'start': 0, 'end': 2}}, 'item': {'Primitive': {'String': 'Dockerfile'}}}, {'tag': {'anchor': None, 'span': {'start': 0, 'end': 2}}, 'item': {'Primitive': {'String': 'nu_plugin_hello'}}}, {'tag': {'anchor': None, 'span': {'start': 0, 'end': 2}}, 'item': {'Primitive': {'String': 'Dockerfile.standalone'}}}]]}

Examples

• pokemon ascii pokemon on demand!
• hello say hello using a sink!

Single Binary

In that you are able to compile your module with pyinstaller (e.g., see examples/len) you can build your python script as a simple binary, and one that doesn't even need nushell installed as a 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!

Important I've found that modules with added data files don't do well (an example is pokemon here!) and that's why we can't uninstall pokemon or nushell. However, I think you would have luck with most text based, simple modules. And of course, you don't have to do this! It's totally ok to keep your Python modules installed alongside nushell, and used when your plugin is executed.

License

This code is licensed under the MPL 2.0 LICENSE.

Help and Contribution

Please contribute to the package, or post feedback and questions as issues.