Batch_replace_fields_values.py

##Batch replace field value=name
##Vector_layer=vector
##Filter_expression=string "name" IS NOT NULL
##Source_field=string name
##Target_field=string short_name
##Replace_layer=table
##Replace_from=string name
##Replace_to=string short_name
##Replace_in_beginning=boolean False
##Replace_before=string
##output=output vector

from qgis.core import *
from processing.core.VectorWriter import VectorWriter
import re

# Get vector layer object
layer = processing.getObject(Vector_layer)
provider = layer.dataProvider()
table= processing.getObject(Replace_layer)

# Operate only on feature with a name
qExp = QgsExpression(Filter_expression)
qReq = QgsFeatureRequest(qExp)
features = layer.getFeatures( qReq )

# Create writer
writer = VectorWriter(output, None, provider.fields(),
                      provider.geometryType(), layer.crs())
                      
# Export features
n = layer.featureCount()
for i, feat in enumerate(features):
    progress.setPercentage(int(i *100 / n))
    target = feat[Source_field]

    # Get replacement data
    # Do it inside the loop because an iterator is always destroyed once run
    replaceList = table.getFeatures()    
    for t in replaceList:
        # Replace search string by value
        k = t[Replace_from]
        v = t[Replace_to]
        if Replace_in_beginning:
            k = '^' + k
        if Replace_before:
            k = k + '(' + Replace_before + ')'
            v = v + '\\1'
        r = re.compile(k)
        target = r.sub(v, target)
    
    feat[Target_field] = target
    writer.addFeature(feat)

del writer