PyQgis, Add field to attribute table and Output error

Question

I'm trying to code a script who calculate id of vineyard lines and vines in these lines.

I code with temporary layers, just my final layer will be save. But I'm getting stuck on adding new fields, at line 39, I have an OUTPUT error, and QGIS log says no more. Can you help me ?

This is my code :

##point_layer=vector
##Intervine_distance=number 1.5
##output_layer=output vector

import os, processing
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from qgis.core import *
from qgis.gui import *

# Project Layer in L93

l93 = processing.runalg("qgis:reprojectlayer", point_layer, "EPSG:2154", None)

# Buffer

Dbuf=(Intervine_distance/2)+0.1

buffer = processing.runalg("qgis:fixeddistancebuffer", l93['OUTPUT'], 
Dbuf, 100, False, None )

# Dissolve

dissolve = processing.runalg("qgis:dissolve", buffer['OUTPUT'], True, '',  None) 

# Split

split = processing.runalg('qgis:multiparttosingleparts', dissolve['OUTPUT'], None)

#New Fields

rang = processing.runalg('qgis:addfieldtoattributestable', split['OUTPUT'], "Rang", 0, 3, 0, None)

pied = processing.runalg('qgis:addfieldtoattributestable', rang['OUTPUT'], "Pied", 0, 3, 0, None)

# Some steps remaind to code here

# Reproject Layer in WGS84

processing.runalg("qgis:reprojectlayer", pied, "EPSG:4326", output_layer)

Answer 1

I think you need to replace rang['OUTPUT'] with rang['OUTPUT_LAYER'] instead as the parameters for the qgis:addfieldtoattributestable algorithm reads:

>>>processing.alghelp('qgis:addfieldtoattributestable')
ALGORITHM: Add field to attributes table
    INPUT_LAYER <ParameterVector>
    FIELD_NAME <ParameterString>
    FIELD_TYPE <ParameterSelection>
    FIELD_LENGTH <ParameterNumber>
    FIELD_PRECISION <ParameterNumber>
    OUTPUT_LAYER <OutputVector>

So instead use:

pied = processing.runalg('qgis:addfieldtoattributestable', rang['OUTPUT_LAYER'], "Pied", 0, 3, 0, None)

Then when you reproject, use :

processing.runalg("qgis:reprojectlayer", pied['OUTPUT_LAYER'], "EPSG:4326", output_layer)