Takes text and separates it into a list of words

def separate(text):
    '''Takes text and separates it into a list of words'''
    alphabet = 'abcdefghijklmnopqrstuvwxyz'
    words = text.split()
    standardwords = []
    for word in words:
        newstr = ''
        for char in word:
            if char in alphabet or char in alphabet.upper():
               newstr += char
        if newstr != '':
            standardwords.append(newstr)
    return map(lambda x: x.lower(),standardwords)