Write

# Import the CSV module
import csv

def main():
    # Create an empty dictionary
    dct ={}

    # Read the rows from oldCSV.csv
    with open('oldCSV.csv') as f:
        # Read all the lines
        lines = f.readlines()

        # count to skip the headers
        count = 0

        # For each row read from the file
        for line in lines:
            if(count == 0): #To skip headers
                count += 1
            else:
                # We split the column by using split and comma as delimiter
                # Each column will be stored in the words list
                words = line.split(',')

                # Make sure that the columns read are more than 1
                if(len(words)> 1):
                    dct[words[0]] = [words[1],words[2], words[3].strip()]

    # Similarly we read from newCSV file
    with open('newCSV.csv') as f:
        lines = f.readlines()
        count = 0
        for line in lines:
            if(count == 0): #To skip headers
                count += 1
            else:
                words = line.split(',')
                if(len(words)> 1):
                    # This will overwrite any keys in the dictionary read from OldCSV
                    # At the same time it will add new rows from newCSV
                    dct[words[0]] = [words[1],words[2], words[3].strip()]

    # Headers for writing to oldCSV.csv file
    fields = ['id','Phone Number','Credit Number','Level Complete']

    # writing to csv file
    with open("OldCSV.csv", 'w',newline='') as csvfile:
        # creating a csv writer object
        csvwriter = csv.writer(csvfile)

        # writing the header fields
        csvwriter.writerow(fields)

        # Sort the keys (i.e. IDs) and for each key we write the values to oldCSV.csv
        for key in sorted(dct.keys()):
            # Combine the key + values of that key to write to the CSV file
            # e.g. if '1': ['123','456','789']
            # we will write ['1','123','456','789']
            lst = [key]+dct[key]

            # Write the above combined list
            csvwriter.writerow(lst)

if __name__=='__main__':
    main()