how to insert and replace a list of words in another list or a string in python

Question

I am trying to replace a string with the word [NOUN] on it. I'm clueless!

Here's my code below - which returns lots of errors - the variable story is a string and listOfNouns is a list - so I try and convert the string into a list by splitting it.:

def replacement(story, listOfNouns):   
    length = len(story1)
    story1 = story.split()
    for c in range(0,len(story1)):
        if c in listOfNouns:
             story1[c]= 'NOUN'
             story = ''.join(story)      
    return story

Here's the error message that I get below when I call the above function with
replacement("Let's play marbles", ['marbles']) :

Traceback (most recent call last):
  File "<pyshell#189>", line 1, in <module>
    replacement("Let's play marbels", ['marbels'])
  File "C:/ProblemSet4/exam.py", line 3, in replacement
    length = len(story1)
UnboundLocalError: local variable 'story1' referenced before assignment

How can I replace the new story1 list with another element from another list?

How do I modify the tuples and return the new string - which is supposed to say:
Let's play [NOUN] ???

Can anyone please help out? I'm lost and i've been trying this for hours using all the knowledge I have in Python/Java to figure this crap out!

Answer 1

Here's a shorter and simpler way of solving your problem.

def replacement(story, nouns):
    return ' '.join('[NOUN]' if i in nouns else i for i in story.split())

Output

In [4]: replacement('Let\'s play marbles, I\'m Ben', ['marbles', 'Ben'])
Out[4]: "Let's play [NOUN], I'm [NOUN]"

Answer 2

The error "referenced before assignment" refers to this:

length = len(story1)
story1 = story.split()

You should first assign story1, then get its length.

Answer 3

The problem is from calculating the length of story1 before setting the value of story1.

Here's a fixed version that also iterates in a more "pythonic" way and fixes the bug of joining the original string and not the split string.

def replacement(story, listOfNouns):   
    story1 = story.split()
    for i,word in enumerate(story1):
        if word in listOfNouns:
             story1[i] = '[NOUN]'
    return ' '.join(story1)      

print(replacement("Let's play marbles", ['marbles']))

Output:

Let's play [NOUN]

Here's another solution that efficiently replaces all instances of the words at once using a regular expression, without replacing parts of words containing the word.

import re

stories = [
    'The quick brown fox jumped over the foxy lady.',
    'Fox foxy fox lady ladies lady foxy fox']

def replacement(story, listOfNouns):
    story = re.sub(r'''
        (?ix)   # ignore case, allow verbose regular expression definition
        \b      # word break
        (?:{})  # non-capturing group, string to be inserted
        \b      # word break
        '''.format('|'.join(listOfNouns)),'[NOUN]',story) # OR all words.
    return story

for story in stories:
    print(replacement(story,'fox lady'.split()))

Output:

The quick brown [NOUN] jumped over the foxy [NOUN].
[NOUN] foxy [NOUN] [NOUN] ladies [NOUN] foxy [NOUN]