python - DictReader get a value when a column # and row # are known -

i given csv file looks this

id, name, age, city 1, andy, 25, ann arbor 2, bella, 40, los angeles 3, cathy, 13, eureka ... ... 

if want city of id=3, eureka example. there way efficiently instead of iterating each row? php code executing python script each time value, , feel being inefficient loop through csv file every time.

iterate on file once , save data dictionary:

data = {} open('input.csv') fin:     reader = csv.dictreader(fin)     record in reader:         data[record['id']] = {k:v k,v in record.items() if k <> 'id'} 

then access required key in dictionary:

print data[3]['city'] # eureka 

in case want persist data in key:value format can save json file:

import json import csv  j = {} open('input.csv') fin:     reader = csv.dictreader(fin)     record in reader:         j[record['id']] = {k:v k,v in record.items() if k <> 'id'} open('output.json','w') fout:     json.dump(j,fout)