urllib.parse.urljoin() might help. It does a join, but it is smart about it and handles both relative and absolute paths. Note this is python 3 code.
>>> import urllib.parse
>>> base="https://www.example-page-xl.com"
>>> urllib.parse.urljoin(base, "https://stackoverflow.com/helloworld/index.php")
'https://www.example-page-xl.com/helloworld/index.php'
>>> urllib.parse.urljoin(base, 'https://www.example-page-xl.com/helloworld/index.php')
'https://www.example-page-xl.com/helloworld/index.php'