>>> line='//.www.google.ru/'
>>> line.strip('/')
'.www.google.ru'

>>> line='//.www.google.ru/'
>>> line.replace('//','')
'.www.google.ru/'

url="http://www.python.su//forum/"

"://"

url = "http://www.python.su//forum/"
url = url.replace('://', ':\\\\').replace('//', '/').replace(':\\\\', '://')

>>> url = "http://www.python.su//forum//////////lalala//"
>>> url = url.replace('://', ':\\\\').replace('//', '/').replace(':\\\\', '://')
>>> url
'http://www.python.su/forum/////lalala/'

import re
url = re.sub(r'(?<!:)/{2,}', '/', url)

url = url.replace('://', ':\\\\').replace('//', '/').replace(':\\\\', '://')

url = "http://www.python.su//forum//////////lalala//"
url = url.replace('://', ':\\\\')
while url.find('//') != -1:
    url = url.replace('//', '/')
url = url.replace(':\\\\', '://')

url = "http://www.python.su//forum//////////lalala//"
newurl = ''
for n, i in enumerate(url):
    if n > 1 and i == '/' and url[n-1] == '/' and url[n-2:n] != ':/':
        continue
    newurl += i
print newurl