((http:\/\/|https:\/\/)([a-z0-9_-]+\.){1,4}[a-z]+)

 [('https://wordpress.org', 'https://', 'wordpress.')]

>>> a = re.match('((http:\/\/|https:\/\/)([a-z0-9_-]+\.){1,4}[a-z]+)', 'https://wordpress.ru')
>>> a.groups()
('https://wordpress.ru', 'https://', 'wordpress.')
>>> a.groups()[0]
'https://wordpress.ru'
>>> a.group()
'https://wordpress.ru'

((?:http:\/\/|https:\/\/)(?:[a-z0-9_-]+\.){1,4}[a-z]+)

https?:\/\/(\w-?)+(\.[a-z]+){1,3}

>>> a = re.search('https?:\/\/(\w-?)+(\.[a-z]+){1,3}}', 'https://wordpress.ru/')
>>> a.group()
'https://wordpress.ru'

>>> a = re.search('https?:\/\/(\w-?)+(\.[a-z]+){1,3}', 'https://word--press.ru/')
>>> a.group()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'group'

a = re.search('https?:\/\/(\w-*)+(\.[a-z]+){1,3}', 'https://word--press.ru/')

https?:\/\/[\w-]+(\.[a-z]+){1,3}

r'https?:// ... '