Question

Using Python I am trying to analyze a tab delimited file. I open the file and import as a list of dictionaries here:

import csv
fileIN = open('transaction_tmp', "r")
list_of_dicts = list(csv.DictReader(fileIN, dialect='excel-tab'))

I need to count (and note the row) for a particular column of this file. I create an empty dictionary:

dict_card = {}

And now I am trying to iterate through the list of dictionaries, and if a value is not noted, I note it (as the key) and for value set the row found (in the list of dictionaries). If it has already been added, I just add the row found:

for x in list_of_dicts:
    if dict_card.has_key(x["CARD_NUMBER"]):
        dict_card[x["CARD_NUMBER"]].append(x)
    else:
        dict_card[x["CARD_NUMBER"]] = x

This last bit of code is giving me an error:

Traceback (most recent call last):
  File "<stdin>", line 3, in ?
AttributeError: 'dict' object has no attribute 'append'

I am having trouble locating my error. Being new to Python, I’m not entirely sure if the way in which I’m accessing list_of_dicts is correct.

Answer 1

This is caused because you are assigning just x to the dict value, instead of [x], a list containing only x. You cannot append something to type x, only lists. To fix, change dict_card[x["CARD_NUMBER"]] = x to dict_card[x["CARD_NUMBER"]] = [x].
Alternatively, just use

for x in list_of_dicts:
    dict_card.setdefault(x['CARD_NUMBER'], []).append(x)