extensions/script/README.md

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# Apache NiFi - MiNiFi - Python Processors Readme


This readme defines the configuration parameters to use ExecutePythonProcessor to run native python processors.

## Table of Contents

- [Description](#description)
- [Configuration](#configuration)

## Description

Python native processors can be updated at any time by simply adding a new processor to the directory defined in
the configuration options. The processor name, when provided to MiNiFi C++ and any C2 manifest will be that
of the name of the python script. For example, "AttributePrinter.py" will be named and referenced in the flow
as "org.apache.nifi.minifi.processors.AttributePrinter" 

Methods that are enabled within the processor are  describe, onSchedule, onInitialize, and onTrigger. 

Describe is passed the processor and is a required function. You must set the description like so:

```python
def describe(processor):
  processor.setDescription("Adds an attribute to your flow files")
```
   
onInitialize is also passed the processor reference and can be where you set properties. The first argument is the property display name,
followed by the description, and default value. The last two arguments are booleans describing if the property is required or requires EL.

```python
def onInitialize(processor):
  processor.setSupportsDynamicProperties()
  processor.addProperty("property name","description","default value", True, False)
```

The onSchedule function is passed the context and session factory. This should be where your processor loads and reads properties via
the getProperty function. onTrigger is executed and passed the processor context and session. You may keep state within your processor.

Much like C++ processors, callbacks may be defined for reading/writing streams of data through the session. Those callback classes will
have a process function that accepts the input stream. You may use codecs getReader to read that data as in the example, below, from
VaderSentiment

```python
class VaderSentiment(object):
  def __init__(self):
    self.content = None

  def process(self, input_stream):
    self.content = codecs.getreader('utf-8')(input_stream).read()
    return len(self.content)
```

## Configuration

To enable python Processor capabilities, the following options need to be provided in minifi.properties. The directory specified
can contain processors. Note that the processor name will be the reference in your flow. Directories are treated like package names.
Therefore if the nifi.python.processor.dir is /tmp/ and you have a subdirectory named packagedir with the file name file.py, it will
produce a processor with the name org.apache.nifi.minifi.processors.packagedir.file. Note that each subdirectory will append a package 
to the reference class name. 

    in minifi.properties
	#directory where processors exist
	nifi.python.processor.dir=XXXX
	
	
## Processors
The python directory (extensions/pythonprocessors) contains implementations that will be available for flows if the required dependencies
exist.
   
## Sentiment Analysis

The SentimentAnalysis processor will perform a Vader Sentiment Analysis. This requires that you install nltk and VaderSentiment
		pip install nltk
		pip install VaderSentiment