Trigrams are a special case of the n-gram, where n is 3. One trigram is a continious sequence of 3 chars in phrase. [Wikipedia](https://en.wikipedia.org/wiki/Trigram)

 - return all trigrams for the given phrase 
 - replace spaces with \_ 
 - return an empty string for phrases shorter than 3

Example:

trigrams('the quick red') ==  the he\_ e\_q \_qu qui uic ick ck\_ k\_r \_re red

Difficulty: introductory

Starter code:

def trigrams(phrase):
	

Solutions:
def trigrams(phrase):
    phrase = phrase.replace(" ", "_")
    return " ".join([phrase[i:i+3]for i in range(len(phrase)-2)])


def trigrams(phrase):
    solution = ''
    if len(phrase) < 3:
        return solution
    phrase = phrase.replace(' ','_')
    for i in range(len(phrase)-2):
        solution = solution + ' ' + phrase[i:i+3]
    return solution[1:]

def trigrams(phrase):
    phrase = phrase.replace(' ', '_')
    return ' '.join(''.join(xs) for xs in zip(phrase, phrase[1:], phrase[2:]))

def trigrams(phrase):

  s = phrase.replace(' ', '_')

  return ' '.join(s[i:i+3] for i in range(len(s)-2))

def trigrams(p):
   r=""
   for i in range(len(p)-2):
      r+=p[i:i+3].replace(" ","_")+" "
   return r.strip()

def trigrams(phrase):
    p = phrase.replace(' ','_')
    return ' '.join([p[i:i+3] for i in range(len(p)-2)])


def trigrams(s):
    return ' '.join([''.join(w).replace(' ', '_') for w in list(zip(s, s[1:], s[2:]))]) if len(s) > 2 else ''

def trigrams(phrase):
    if len(phrase) < 3: return ''
    phrase = phrase.replace(" ", "_")
    chars = [x for x in phrase]
    trigram = []
    for x in range(1, len(chars) - 1):
        trigram.append(chars[x-1] + chars[x] + chars[x+1])
    return ' '.join(trigram)

def trigrams(phrase):
    svar = ''
    if len(phrase)<3:
        return ''
    else:
        phrase = phrase.replace(" ", "_")
        for i in range(len(phrase)-2):
            svar = svar + ' ' + phrase[i:i+3]
        return svar[1:]
        


def trigrams(phrase):
    if len(phrase) < 3:
        return ''
    phrase = phrase.replace(' ', '_')
    ret = []
    for i in range(len(phrase) - 2):
        ret.append(phrase[i:i + 3])
    return ' '.join(ret)