How do I add a list of dictionaries to another list of dictionaries?

Question

I'm using a for loop to add a dictionary to a list of dictionaries (which I'm calling data_file), using data_file.append()

It works fine :) But then later I try to add some more dictionaries to data_file in another for loop and I use data_file.append() again and it doesn't work. It doesn't add those dictionaries to data_file

Does anyone know what I'm doing wrong?

I don't get an error. It just produces a file that only has the dictionaries from massage_generators. It doesn't take on anything from travel_generators.

I've even tried commenting out the first for loop, the one for massage_generators, and in that case it does add in the travel_generators dictionaries. It's like I can't use .append() twice?

Any help would be much appreciated please!

I'm sorry it's not very elegant, I'm only just learning this coding stuff! :)

Thanks

import csv
import copy
import os
import sys


generators = list()

for filename in os.listdir(os.getcwd()):
    root, ext = os.path.splitext(filename)
    if root.startswith('Travel Allowance Auto Look up') and ext == '.csv':
      travel = filename

open_file = csv.DictReader(open(travel))
generators.append(open_file)    

travel_generators = generators[:]
massage_generators = generators[:]

data_file = []  # result will be stored here (List of dicts)


travel_remap = {'FINAL_TRAVEL_ALL':'AMOUNT'}
massage_remap = {'MASSAGE_BIK':'AMOUNT'}


for generator in massage_generators:
  for dictionary in generator:
    dictionary['PAYMENT_TYPE_CODE'] = 'MASSAGE_BIK'
    dictionary['COMMENT'] = 'Massage BIK'
    dictionary['IS_GROSS'] = 'FALSE'
    dictionary['PAYMENT_TO_DATE'] = '01/01/2099'
    dictionary['PAID MANUALLY'] = 'FALSE'
    for old_key, new_key in massage_remap.iteritems():
      if old_key not in dictionary:
        continue
      dictionary['AMOUNT'] = dictionary['MASSAGE_BIK']
      del dictionary['MASSAGE_BIK']
      if (dictionary['AMOUNT'] != '0' and dictionary['AMOUNT'] != ''):
          data_file.append(dictionary)

for generator in travel_generators:
  for dictionary in generator:
    dictionary['PAYMENT_TYPE_CODE'] = 'TRANSPORTATION_ALLOWANCE'
    dictionary['COMMENT'] = 'Annual travel allowance paid in monthly installments'
    dictionary['IS_GROSS'] = 'TRUE'
    dictionary['PAYMENT_TO_DATE'] = '01/01/2099'
    dictionary['PAID MANUALLY'] = 'FALSE'
    for old_key, new_key in travel_remap.iteritems():
      if old_key not in dictionary:
        continue
      dictionary['AMOUNT'] = dictionary['FINAL_TRAVEL_ALL']
      del dictionary['FINAL_TRAVEL_ALL']
      if (dictionary['AMOUNT'] != 'Not Applicable' and dictionary['AMOUNT'] != '0' and dictionary['AMOUNT'] != '' and dictionary['AMOUNT'] != '#N/A'):
          data_file.append(dictionary)


keys = ['EMPID', 'Common Name', 'PAYMENT_TYPE_CODE', 'CURRENCY', 'AMOUNT', 'EFFECTIVE_DATE',
        'COMMENT', 'PAYMENT_FROM_DATE', 'PAYMENT_TO_DATE', 'IS_GROSS', 'HIDDEN_UNTIL', 'PAID MANUALLY', 'PAYMENT_DATE']

bulk_upload = open('EMEA Bulk Upload.csv', 'wb')
dict_writer = csv.DictWriter(bulk_upload, keys, restval='', extrasaction='ignore')
dict_writer.writer.writerow(keys)
dict_writer.writerows(data_file)

print "Everything saved! Look up EMEA Bulk Upload.csv"

Answer 1

Here's your problem:

open_file = csv.DictReader(open(travel))
generators.append(open_file)    

travel_generators = generators[:]
massage_generators = generators[:]

Your travel_generators and massage_generators lists are using the same open file to iterate over and get data; the problem with that is once the file has been iterated over once by the csv.DictReader in massage_generators it has been exhausted and you get no more data when you try to read it again in travel_generators .

Try this instead:

generators.append(travel)     # just the filename    

travel_generators = generators[:]
massage_generators = generators[:]

and then in your loops:

for filename in massage_generators:
    for dictionary in csv.DictReader(open(filename)):

Also, in your first loop where you are gathering filenames: be aware that the loop is only saving the last filename that matches. If that is your intention you can make it clear by adding break on the line after travel = filename .

Answer 2

In the example you provided, generators , travel_generators , and massage_generators are all identical, and each contain the same instance of open_file . When you iterate massage_generators , you reach the end of the file. Then when you iterate travel_generators , there's nothing left to iterate in open_file .

At the very least, you could change the following line:

open_file = csv.DictReader(open(travel))

To:

open_file = map(None, csv.DictReader(open(travel)))

open_file is now a list and not a generator and can be iterated and re-iterated.

However, I would recommend you iterate through the file once, and build your two dictionaries, and write to a DictWriter instance in each iteration.

open_file = csv.DictReader(open(travel))
...
dict_writer = csv.DictWriter(bulk_upload, keys, restval='', extrasaction='ignore')
dict_writer.writer.writerow(keys)

for line in open_file:
    massage_dictionary={}
    massage_dictionary.update(line)
    ... # manipulate massage_dictionary
    dict_writer.writerow(massage_dictionary)

    travel_dictionary={}
    travel_dictionary.update(line)
    ... # manipulate travel_dictionary
    dict_writer.writerow(travel_dictionary)