URLField does not support url with underscore

[guoqiao]

if your url has a '_' in it, like this:
​http://django_compressor.readthedocs.org/
the URLField will complain that it is not a valid url. the problem lies in the '_' symbol. I find in the source code as Following:
class URLValidator(RegexValidator):

regex = re.compile(

r'^{(?:http|ftp)s?:' # ​http:// or ​https://
r'(?:(?:[A-Z0-9](?:[A-Z0-9-]{0,61}[A-Z0-9])?\.)+(?:[A-Z]{2,6}\.?|[A-Z0-9-]{2,}\.?)|' #domain...
r'localhost|' #localhost...
r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})' # ...or ip
r'(?::\d+)?' # optional port
r'(?:/?|/\S+)$', re.IGNORECASE)}

the related part is this line:
r'(?:(?:[A-Z0-9](?:[A-Z0-9-]{0,61}[A-Z0-9])?\.)+(?:[A-Z]{2,6}\.?|[A-Z0-9-]{2,}\.?)|'
It's clear that '_' is not included in the pattern.
I think this is not reaonable for there's a lot of url has a '_' in it.