Hi i\'m trying to stem words with a python stemmer, i tried Porter and Lancaster, but they have the same problem. They can\'t stem correclty words that end with \"er\" or \"e\".
To quote the page on Wikipedia, In computational linguistics, a stem is the part of the word that never changes even when morphologically inflected, whilst a lemma is the base form of the word. For example, given the word "produced", its lemma (linguistics) is "produce", however the stem is "produc": this is because there are words such as production.
So your code is likely giving you correct results. You seem to expect a lemma which is not what a stemmer produces (except when the lemma happens to equal the stem)