From noun to verb

[wavic]

You check against an empty list. It evaluates to False:

In [1]: bool([])
Out[1]: False

So you can just:

    try:
        if noun[-2:] == "st":
            poss_verb = noun.lower() + "eln"
            if gn.synsets(poss_verb, pos='v'):
                poss_verb = noun.lower() + "ern"

            if gn.synsets(poss_verb, pos='v'):
                poss_verb = noun.lower().replace('u', 'ü') + "eln"

            if gn.synsets(poss_verb, pos='v'):
                poss_verb = noun.lower().replace('a', 'ä') + "igen"

            return poss_verb
 
    except:
        return None