Don't use `for line in file.readlines():`, do `for line in file:` instead. Don't use `map(writer.writerow, data)`, do `writer.writerows(data)` instead. Use bin

Don't use `for line in file.readlines():`, do `for line in file:` instead. Don't use `map(writer.writerow, data)`, do `writer.writerows(data)` instead. Use binary mode for csv files in Python 2, use newline='' in Python 3. You forgot to open the first output file in the write mode.