>>> import pywikibot
>>> s = pywikibot.Site()
>>> s.login()
>>> s
APISite("de", "wikipedia")
>>> s = pywikibot.Site('skr')
>>> s
APISite("skr", "wikipedia")
>>> s.login()
Traceback (most recent call last):
  File "C:\pwb\GIT\core\pywikibot\login.py", line 115, in __init__
    user = code_to_usr.get(site.code) or code_to_usr['*']
KeyError: '*'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<pyshell#55>", line 1, in <module>
    s.login()
  File "C:\pwb\GIT\core\pywikibot\tools\__init__.py", line 1480, in wrapper
    return obj(*__args, **__kw)
  File "C:\pwb\GIT\core\pywikibot\site\__init__.py", line 327, in login
    login_manager = api.LoginManager(site=self, user=self.username())
  File "C:\pwb\GIT\core\pywikibot\tools\__init__.py", line 1480, in wrapper
    return obj(*__args, **__kw)
  File "C:\pwb\GIT\core\pywikibot\login.py", line 117, in __init__
    raise NoUsername(
pywikibot.exceptions.NoUsername: ERROR: username for wikipedia:skr is undefined.
If you have a username for that site, please add a line to user-config.py as follows:
usernames['wikipedia']['skr'] = 'myUsername'
>>>