How to Export formatted CSV data to file?

Question

I have a python script that parses/prints all the urls from an xml file to csv format. It does this, but it doesn't create an actual csv file. How do I turn this into an actual csv file?

Here's the script repo https://github.com/daveoconnor/site-map-parser

Here's the code:

from sitemapparser import SiteMapParser
import pandas as pd
import csv

sm = SiteMapParser('https://shop.busybeaver.com/sitemaps/bb_shop_sitemap.xml')    # reads /sitemap.xml
if sm.has_sitemaps():
    sitemaps = sm.get_sitemaps() # returns iterator of sitemapper.Sitemap instances
else:
    urls = sm.get_urls()         # returns iterator of sitemapper.Url instances


    from sitemapparser.exporters import CSVExporter

# sm set as per earlier library usage example

csv_exporter = CSVExporter(sm)
if sm.has_sitemaps():
    print(csv_exporter.export_sitemaps())
elif sm.has_urls():
    print(csv_exporter.export_urls())

And here's the Class used to for mat the data (CSVExporter):

import csv
import io
from ..exporter import Exporter
from ..url import Url
from ..sitemap import Sitemap
from datetime import datetime


class CSVExporter(Exporter):
    short_name = 'csv'

    def export_sitemaps(self):
        """
        returns csv data with format:
        url: string
        lastmod: ISO8601 format date
        """
        buffer = io.StringIO()
        writer = csv.DictWriter(
            buffer,
            delimiter=",",
            fieldnames=Sitemap.fields,
            quoting=csv.QUOTE_NONNUMERIC
        )
        writer.writeheader()
        for sm in self.data.get_sitemaps():
            row = {}
            for field in Sitemap.fields:
                v = getattr(sm, field)
                row[field] = v if type(v) is not datetime else v.isoformat()
            writer.writerow(row)

        return buffer.getvalue().rstrip()

    def export_urls(self):
        """
        returns csv data with format:
        url: string
        lastmod: ISO8601 format date
        changefreq: string
        priority: float, 0-1
        """
        buffer = io.StringIO()
        writer = csv.DictWriter(
            buffer,
            delimiter=",",
            fieldnames=Url.fields,
            quoting=csv.QUOTE_NONNUMERIC
        )
        writer.writeheader()
        for url in self.data.get_urls():
            row = {}
            for field in Url.fields:
                v = getattr(url, field)
                row[field] = v if type(v) is not datetime else v.isoformat()
            writer.writerow(row)

        return buffer.getvalue().rstrip()

--UPDATE

added to bottom:

open('file.csv', 'w').write(csv_exporter.export_urls())

This creates a csv, but there is an extra row between each url. How can I write without that extra row?