Make a dictionary with duplicate keys in Python

Question

I have the following list which contains duplicate car registration numbers with different values. I want to convert it into a dictionary which accepts this multiple keys of car registration numbers.

So far when I try to convert list to dictionary it eliminates one of the keys. How do I make a dictionary with duplicate keys?

The list is:

EDF768, Bill Meyer, 2456, Vet_Parking
TY5678, Jane Miller, 8987, AgHort_Parking
GEF123, Jill Black, 3456, Creche_Parking
ABC234, Fred Greenside, 2345, AgHort_Parking
GH7682, Clara Hill, 7689, AgHort_Parking
JU9807, Jacky Blair, 7867, Vet_Parking
KLOI98, Martha Miller, 4563, Vet_Parking
ADF645, Cloe Freckle, 6789, Vet_Parking
DF7800, Jacko Frizzle, 4532, Creche_Parking
WER546, Olga Grey, 9898, Creche_Parking
HUY768, Wilbur Matty, 8912, Creche_Parking
EDF768, Jenny Meyer, 9987, Vet_Parking
TY5678, Jo King, 8987, AgHort_Parking
JU9807, Mike Green, 3212, Vet_Parking

The code I have tried is:

data_dict = {}
data_list = []

def createDictionaryModified(filename):
  path = "C:UsersuserDesktop"
  basename = "ParkingData_Part3.txt"
  filename = path + "//" + basename
  file = open(filename)
  contents = file.read()
  print contents,"
"
  data_list = [lines.split(",") for lines in contents.split("
")]
  for line in data_list:
    regNumber = line[0]
    name = line[1]
    phoneExtn = line[2]
    carpark = line[3].strip()
    details = (name,phoneExtn,carpark)
    data_dict[regNumber] = details
  print data_dict,"
"
  print data_dict.items(),"
"
  print data_dict.values()

Answer 1

Python dictionaries don't support duplicate keys. One way around is to store lists or sets inside the dictionary.

One easy way to achieve this is by using defaultdict:

from collections import defaultdict

data_dict = defaultdict(list)

All you have to do is replace

data_dict[regNumber] = details

with

data_dict[regNumber].append(details)

and you'll get a dictionary of lists.