Writing your first kedro Nodes
==============================

https://youtu.be/-gEwU-MrPuA

Date: September 13, 2021

https://youtu.be/-gEwU-MrPuA

Before we jump in with anything crazy, let's make some nodes with some vanilla
data structures.

## import node

You will need to import node from kedro.pipeline to start creating nodes.

``` python
from kedro.pipeline import node
```

## func

The `func` is a callable that will take the `inputs` and create the `outputs`.

## inputs / outputs

Inputs and outputs can be None, a single catalog entry as a string, mutiple
catalog entries as a List of strings, or a dictionary of strings where the key
is the keyword argument of the func and the value is the catalog entry to use
for that keyword.

## our first node

Sometimes in our pipelines our data is coming from an api where we already have
python functions built to pull with. Thats ok, kedro supposrts that with
`inputs=None`.

``` python
def create_range():
 return range(100)

make_range = node(
 func=create_range,
 inputs=None,
 outputs='range'
 )
```

## second node

Now we have some data to work from, lets use that as our input.

``` python
def square_range():
 return [i**2 for i in range]

square_range = node(
 func=square_range,
 inputs='range',
 outputs='range_squared'
 )
```

## Multiple Inputs

Kedro can take lists or dicts as either input or output when your function
needs more than one input or output.

``` python
def concat(range, range_two):
 return [*range, *range_two]

concat_ranges = node(
 func=concat,
 inputs=['range', 'range_squared']
 outputs='concat'
 )

## inputs could also be defined as a dict
concat_ranges = node(
 func=concat,
 inputs={'range': 'range', 'range_two': 'range_squared'}
 outputs='concat'
 )
```

## Links

* [all of my kedro articles](https://waylonwalker.com/kedro/)
* [kedro playlist on YouTube](https://www.youtube.com/watch?v=bw5_FWDVRpU&list=PLTRNG6WIHETCoPt5gAKYSH_HCZvE_r41n)
* [node docs](https://kedro.readthedocs.io/en/stable/kedro.pipeline.node.html)
* [first_nodes.py](https://gist.github.com/WaylonWalker/347b32c6ae7b799d1e0853c3811a98de)