updateLocatoins.py

import csv

#Extracts data from Postcodes districts file and turns it into a list of lists
def locationsGenerator():
    with open('Postcode districts.csv', 'r') as csv_file: #Postcode districts from https://www.doogal.co.uk/postcodedownloads.php
        csv_reader = csv.reader(csv_file)

        next(csv_reader)

        locations = []
        for line in csv_reader:
            newline = []

            for entity in line:
                entity = entity.lower()
                newline.append(entity)
            locations.append(newline)
        return locations

#Extracts data from Admin areas file and turns it into a list of lists
def otherCSV():
    with open('Admin areas.csv', 'r') as csv_file:  #Admin areas from https://www.doogal.co.uk/postcodedownloads.php (List of countries and administative areas with population data)
        csv_reader = csv.reader(csv_file)

        next(csv_reader)

        adminAreasList = []
        for line in csv_reader:
            newLine = []

            for entity in line:
                entity = entity.lower()
                newLine.append(entity)
            adminAreasList.append(newLine)
        return adminAreasList

#Function to add in the area code of the region to the postcodes list
def addCode(locations, codes):
    newPostcodesList = []
    lastAdded = "s12000034" #The first code in the admin areas file

    #Goes through each postcode. Checks each region of each postcode, and if that matches with a region in the admin areas list, it adds the corresponding area code to the postcode list
    for line in locations:
        for codeLine in codes:
            if line[2] == codeLine[0]:
                line[5] = codeLine[2]
                lastAdded = line[5]
            #If the postcode region does not match with a region from the admin areas list, it looks at the previously added code, assumes that is the correct code, and adds it to the postcode list
            if line[5] == "":
                line[5]=lastAdded
        newPostcodesList.append(line)
    return newPostcodesList

#Constructs lists from CSV files for the addCode function
postcodesList = locationsGenerator()
adminAreasList = otherCSV()
newPostcodesList = [["Postcode", "Town/Area", "Region", "Population", "Households", "Code"]] + addCode(postcodesList, adminAreasList)  #Adds headers of collumns then updated postcode list

#Writes the new postcodes list with the correct codes to a new file to be used by the main body of code https://stackoverflow.com/questions/14037540/writing-a-python-list-of-lists-to-a-csv-file
with open('locations.csv', 'w', newline="") as f:
    writer = csv.writer(f)
    writer.writerows(newPostcodesList)