Run regexp in PyQGIS script?

Question

Using QGIS version 2.18.11 I have an attribute table with a column of over 500K of records that has many missing spellings, abbreviations and erroneous characters that I need cleaned up on a regular basis. I can use regexp in the field calculator but can only run one expression at a time. I need to run approximately 150 expressions.
Like:

regexp_replace("DirtyNames" ,'([-\/~!@#$%^&*{}:"<>?|/.,;=_+]?)', '') and regexp_replace("DirtyNames" ,'TRL', 'TRAIL')

I’m thinking a Python script would likely be the easiest way to do this but don’t know the Python language. The table is "Local_Streets". The field is "DirtyNames" and the regexp results would go to the "CleanedNames" field.

# Run_Regexp_Statements
####################################
from qgis.utils import iface
from PyQt4.QtCore import QVariant
_DIRTY_FIELD = 'DirtyNames'
_CLEAN_FIELD = 'CleanedNames'
layer = iface.activeLayer()
layer.startEditing()
# Create a field to store the results
layer.dataProvider().addAttributes(
 [QgsField(_CLEAN_FIELD, QVariant.String),
layer.updateFields()
# **WHAT NEEDS TO GO HERE to be able to run the regexp’s ?**
# regexp_replace("DirtyNames" ,'([-\/~!@#$%^&*{}:"<>?|/.,;=_+]?)', '')
# regexp_replace("DirtyNames" ,'TRL', 'TRAIL')
Layer.commitChanges()
print 'Processing complete.'

Answer 1

You'll need the re library.

import re
replaced = re.sub(r'([-\/~!@#$%^&*{}:"<>?|/.,;=_+]?)',r'replacementpattern',dirty_line))

More info.

• gisnside: Can the following line be : replaced = re.sub('TRL','TRAIL',replaced) (and so on) in your code ?
• Phil_in_Tx: Thanks Ena2345 and gisnside for your replies. I get a invalid syntax error on both. I looked at the link provided by Ena but I'm not really following what I'm doing wrong.<br> import re<br> replaced = re.sub('TRL','TRAIL',r'replacementpattern',_DIRTY_FIELD)
• Piskr: Well the reason why it doesn't work is because it only works for 1 value at the time. So if you looped through the layer you could do it. But such operation should cost you O(n). I don't know how much such operations delay on QGIS so I cannot estimate the time taken.