Question

I am still struggling with understanding classes, I am not certain but I have an idea that this function I have created is probably a good candidate for a class. The function takes a list of dictionaries, identifies the keys and writes out a csv file.

First Q, is this function a good candidate for a class (I write out a lot of csv files

Second Q If the answer to 1 is yes, how do I do it

Third Q how do I use the instances of the class (did I say that right)

import csv
def writeCSV(dictList,outfile):
    maxLine=dictList[0]
    for item in dictList:
        if len(item)>len(maxLine):
            maxLine=item
    dictList.insert(0,dict( (key,key) for key in maxLine.keys()))

    csv_file=open(outfile,'ab')
    writer = csv.DictWriter(csv_file,fieldnames=[key for key in maxLine.keys()],restval='notScanned',dialect='excel')
    for dataLine in dictList:
        writer.writerow(dataLine)
    csv_file.close()
    return

Answer 1

If you want to write a lot of CSV files with the same dictList (is that what you’re saying…?), turning the function into a class would let you perform initialization just once, and then write repeatedly from the same initialized instance. E.g., with other minor opts:

class CsvWriter(object):

  def __init__(self, dictList):
    self.maxline = max(dictList, key=len)
    self.dictList = [dict((k,k) for k in self.maxline)]
    self.dictList.extend(dictList)

  def doWrite(self, outfile):
    csv_file=open(outfile,'ab')
    writer = csv.DictWriter(csv_file,
                            fieldnames=self.maxLine.keys(),
                            restval='notScanned',
                            dialect='excel')
    for dataLine in self.dictList:
        writer.writerow(dataLine)
    csv_file.close()

This seems a dubious use case, but if it does match your desire, then you’d instantiate and use this class as follows…:

cw = CsvWriter(dataList)
for ou in many_outfiles:
  cw.doWrite(ou)