OS Codepoint file reader, Released under the CC0 license.

codepoint.py

#OS Codepoint file reader, by Tim Sheerman-Chase 2018
#Released under the CC0 license.
import zipfile
import csv
import os
import io

#Get Code point open from https://www.ordnancesurvey.co.uk/business-and-government/products/code-point-open.html

def ReadCodePoint(fi, callback):
	for info in fi.infolist():
		pathSp = os.path.split(info.filename)
		if pathSp[0] != "Data/CSV":
			continue

		rawFile = io.StringIO(fi.read(info.filename).decode('utf-8'))
		fileData = csv.reader(rawFile, lineterminator="\n")

		for li in fileData:
			callback(li)

class CodePointMemStore(object):
	def __init__(self):
		self.postcodes = {}

	def __call__(self, val):
		po1, po2 = val[0][:4].strip(), val[0][4:]
		self.postcodes[(po1, po2)] = list(map(int, val[2:4]))

def UpdatePostcodeList(fina, memStore, outFina):
	#Takes a list of postcodes and appends eastings and northings

	fi = csv.reader(open(fina, "rt"))
	fiout = csv.writer(open(outFina, "wt"))
	for li in fi:
		po1, po2 = li[0][:4].strip().upper(), li[0][4:].strip().upper()
		eastnorth = memStore.postcodes[(po1, po2)]
		print (po1, po2, eastnorth)
		fiout.writerow(li+eastnorth)
	del fi
	del fiout

if __name__=="__main__":
	data = zipfile.ZipFile('codepo_gb.zip')
	memStore = CodePointMemStore()
	ReadCodePoint(data, memStore)

	UpdatePostcodeList('mempostcodes.txt', memStore, 'mempostcodes2.txt')