When working with a full export it'll contain extra rows called Shopping Cart Item. This script removes such rows and copies the Item Titles of into the Item Title column of the original transaction row.

paypal-combine-rows.py

"""
I hate PayPal. When working with a full export it'll contain extra rows called
Shopping Cart Item. This script removes such rows and copies the Item Titles of
into the Item Title column of the original transaction row.

Usage:
# python paypal-combine-rows.py input_file.csv > output_file.csv
"""
import csv
import sys

filename = sys.argv[1]

try:
    reader = csv.reader(open(filename, 'rb'), delimiter=',', quotechar='"')
    writer = csv.writer(sys.stdout, delimiter=',', quotechar='"')
except IOError as e:
    print e
    exit()

last_txn = ''
last_row = []

# 0-based indices of columns. These may change when PayPal changes.
column_txn = 15
column_item_title = 18

for row in reader:
    if row[column_txn] != last_txn:
        if last_row:
            last_row[column_item_title] = last_row[column_item_title].strip(',')  # Trim the extra commas
            writer.writerow(last_row)

        last_row = row
    else:
        last_row[column_item_title] += ",%s" % row[column_item_title]  # Replace Item Title with a real item title

    last_txn = row[column_txn]