For example have a look to the netext dict in welcome.py. Looking up the 'commons' entry is successful for a site object but it fails for a bare 'commons' code:
>>> import pwb, pywikibot as py >>> from pywikibot.i18n import translate >>> from scripts.welcome import netext >>> s = py.Site('commons', 'commons') >>> translate(s, netext) '{{subst:welcome}} %s' >>> translate('commons', netext) is None True