How to modify word in a for loop in python

Im trying to stem some text in python with SnowballStemmer, but it wont work. Here is the code:

import nltk
from nltk import SnowballStemmer

stem = SnowballStemmer("spanish")

def limpiar (texto):
  texto = texto.split()
  stemm = SnowballStemmer('spanish')
  for palabra in texto:
    palabra = stem.stem(palabra.lower())
    
  return texto

It returns the text in lower capitals, but without stemming

The will work :

import nltk
from nltk.stem.snowball import SnowballStemmer

def limpiar(texto):
    words=texto.split()
    stem_words=[]
    for w in words: 
        x = snow_stemmer.stem(w) 
        stem_words.append(x) 

    #print stemming results 
    for e1,e2 in zip(words,stem_words): 
        print(e1+' ----> '+e2.lower())

snow_stemmer = SnowballStemmer(language='spanish')
texto="..."
limpiar(texto)