Question

So far all I am able to do within the function is store all the data twice over.

import csv
def csvWriter(filename, records): 
  header = []
  for i in records:
    for v in i:
      header.append(v)
  test = open(filename,'w')
  dict_wr = csv.DictWriter(test,header)
  dict_wr.writerow(dict(zip(header,header)))
  for i in records:
    dict_wr.writerow(dict(zip(header,i.values())))
  test.close()
  return '%d records processed.' % len(records)

File contains:

a,b,a,b
1,2,1,2
3,4,3,4

I believe I found the problem, inside the for loop, I’m having trouble creating the proper header.

Answer 1

It looks like your records in this example are 2 dictionaries with the same keys (‘a’ and ‘b’). You can fix this by getting the header from the first dictionary:

for i in records[0]:
    for v in i:             
        header.append(v)

However, if your other records have unique key values, you’ll probably want to include them in the header:

for i in records:
    for v in i:
        if v not in header: header.append(v)

Finally, if you have repeated values in the header, and you have DictWriter write a row, it will repeat entries for each duplicated header value. For example,

import csv
testfile = open("test.csv", "w")
header = ["a","b", "a","b"]                      #duplicate header fields
writer = csv.DictWriter(testfile, header)
writer.writerow(dict(zip(header, header)))
writer.writerow({header[0]:"A", header[1]:"B"})  #notice it writes 4 values to the row
testfile.close()