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円_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")

• Frau Schmidt: I don't know python, but what stands 'e' for? don't see any declaration in your code snippet or is it al global variable?
• Spacedman: Is it a typo for the exp QgsExpression you declared in line ~20?
• Joseph: Sorry, that was a mistake on my part. You shouldn't need that line e.prepare(layer.pendingFields()).
• Joseph: Thanks George but @JochenSchwarze posted an answer which already describes commenting out (or removing) that line so please accept his :)
• Joseph: @GeorgeC - Struggling to find the problem as the code still works and updates the .dbf file. This is after I clear all attributes in the 3 fields you mention in your code and setting the expression to exp = QgsExpression( """ "File_Type" = 'shp' """ ). Don't think I can help much further, sorry -_-

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).

• GeorgeC: I approved this to quick. It appears to work (i.e no errors) but the data fields are not updated. The query works correctly when just run in "select by expression" but not in the code. What else could be wrong?
• Dan: Hello everyone, does this work with QGIS 3.x and python 3? I failed to repeat this successfully.
• GeorgeC: See the updated Q for Python 3x code.