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.

[Claude Paroz]

Reformatted, please use preview before posting the ticket.