QGIS find and then replace value in multiple columns

Question

This is based on a previous question/answer that I had. Replacing values in multiple columns using QGIS Field Calculator?

I need it to update 3 fields now and I get an name 'e' is not defined error. What have I done wrong?

layer = qgis.utils.iface.activeLayer()

# Set field names you want to update
field_1 = "New_Name"
field_2 = "New_File_P"
field_3 = "Process"
idx_1 = layer.fieldNameIndex( field_1 )
idx_2 = layer.fieldNameIndex( field_2 )
idx_3 = layer.fieldNameIndex( field_3 )


# Set expression to find all features which fall into expression
exp = QgsExpression( """ "Existing_F" LIKE '%2015 Aerial Ortho\\_2015\\ECW_Tiles%'  """ )

# Select all features which fall into expression
ids = [i.id() for i in layer.getFeatures(QgsFeatureRequest(exp))]
layer.setSelectedFeatures(ids)

# Set expressions to fill in values for selected features
formula_1 = """ "File_Name" """
formula_2 = """ '\\sipv-gis01\\GIS_Library\\Raster\\Aerial\\2015_25cm\\Images\\ECW' """
formula_3 = """  'y'  """
e_1 = QgsExpression(formula_1)
e_2 = QgsExpression(formula_2)
e_3 = QgsExpression(formula_3)
e.prepare(layer.pendingFields())

with edit(layer):
    # For each selected feature
    for f in layer.selectedFeatures():
        f[idx_1] = e_1.evaluate(f)
        f[idx_2] = e_2.evaluate(f)
        f[idx_3] = e_3.evaluate(f)

        layer.updateFeature(f)

Error

e.prepare(layer.pendingFields())
Traceback (most recent call last):
  File "<input>", line 1, in <module>
NameError: name 'e' is not defined

==== I needed to do this again and here's the QGIS 3x code =====

#search and replace text in all fields of all layers in map

#set text to search for and replace with.
#CAUTION Partial match is allowed
#Based on https://gis.stackexchange.com/questions/317855/search-and-replace-text-in-all-fields-in-qgis-3

searchText = "Bougainvilia"
replaceText = "Bougainvillea"

#run on active layer
#layer = iface.activeLayer()

#run on all layers
layers = QgsProject.instance().mapLayers()
i=1
for layer_id, layer in layers.items():
    print("Layer: %s" % (layer.name()))
    # get data provider
    dpr = layer.dataProvider()
    for field in layer.fields():
        fieldName=field.name()

        for feature in layer.getFeatures():
            inText = str(feature[fieldName])
            # get field index
            fieldIndex = layer.fields().indexFromName(fieldName)
            #print ("Checking %s" % (inText))

            if searchText in inText:
                # change inText
                print ("%s . REPLACED: %s in %s with %s in column: %s" % (i, searchText, inText, replaceText, fieldName))
                outText = inText.replace(searchText, replaceText)
                i+=1
                # save changes
                dpr.changeAttributeValues({feature.id(): {fieldIndex: outText}})
print ("Completed")

Answer 1

According to http://docs.qgis.org/testing/en/docs/pyqgis_developer_cookbook/expressions.html the member function QgsExpression.prepare() is not mandatory but makes the execution faster. I would recommend to comment out the line e.prepare(layer.pendingFields()) and see what happens.

And as far as I see, an exp.prepare(...) is missing directly behind the creation of the expression (i.e. exp=QgsExpression("""...) if things run slow, because the expression is evaluated in the next line as an argument to QgsFeatureRequest(exp).