UnicodeDecodeError possibly with Scandinavian letters

Command:
python3 ~/sitemap/python-sitemap-master/main.py --domain https://www.xetnet.fi --image --output sitemap.xml --verbose
Output:

INFO:root:Start the crawling process
INFO:root:Crawling #1: https://www.xetnet.fi
INFO:root:Crawling #2: https://www.xetnet.fi/category/ror/
INFO:root:Crawling #3: https://www.xetnet.fi/wordpress-asennus-webhotelliin-2/
INFO:root:Crawling #4: https://www.xetnet.fi/category/ruby/
INFO:root:Crawling #5: https://www.xetnet.fi/asiakaspalvelu/reilua-palvelua/
INFO:root:Crawling #6: https://www.xetnet.fi/webhotelli/wordpress-webhotelli/
INFO:root:Crawling #7: https://www.xetnet.fi/wordpress/
INFO:root:Crawling #8: https://www.xetnet.fi/palvelupaketin-vaihtaminen-suurempaan-tai-pienempaan/
Traceback (most recent call last):
File "/home/paivisanteri/sitemap/python-sitemap-master/main.py", line 53, in
crawl.run()
File "/home/paivisanteri/sitemap/python-sitemap-master/crawler.py", line 101, in run
self.__crawling()
File "/home/paivisanteri/sitemap/python-sitemap-master/crawler.py", line 205, in __crawling
print (""+self.htmlspecialchars(url.geturl())+"" + lastmod + image_list + "", file=self.output_file)
UnicodeEncodeError: 'ascii' codec can't encode character '\xe4' in position 745: ordinal not in range(128)

Can this be somehow local problem or maybe in my python settings? I am not familiar with python.