Python find ONLY the first instance of a word in a string

Question

Newbie to Python here. I would like to extract the sentence where the first instance of the words in the list have been found. Currently, it is extracting all strings which have the word 'dog' and 'cat'. I tried (i.split('.')[0]) but this is not working either. Can anyone help please?

text= 'the dog was there. the cat is there too. python is the best. the dog want want want was there. '

lst=[]
words=['dog', 'cat', 'chocolate']
for i in text.split('.'):
    for j in words:
        if j in i:
            print(i.split('.')[0])
            lst.append (i.split('.')[0]) 
else:
    lst.append('na')
    print('na')

Output:

the dog was there

the cat is there too

the dog want want want was there

na

Desired output:

the dog was there

the cat is there too

n/a (because choclate is not found)

thank you!

Answer 1

Without making a lot of changes to your code, your output can be achieved by using 'remove' on your 'words' list.

text= 'the dog was there. the cat is there too. python is the best. the dog want want want was there. '

lst=[]
words=['dog', 'cat', 'chocolate']
for i in text.split('.'):
    for j in words:
        if j in i:
            print(i.split('.')[0])
            words.remove(j) # this will remove the matched element from your search list
            lst.append (i.split('.')[0]) 
else:
    lst.append('na')
    print('na')

Answer 2

If you reverse your loops, you can just use break to go to the next word:

text= 'the dog was there. the cat is there too. python is the best. the dog want want want was there. '

lst=[]
words=['dog', 'cat', 'chocolate']
for j in words: # each word
    for i in text.split('.'):  # each sentence
        if j in i:
            print(i.split('.')[0])
            lst.append (i.split('.')[0]) 
            break  # next word
else:
    lst.append('na')
    print('na')

Output:

the dog was there
 the cat is there too
na

Answer 3

A possible solution could be keeping track of which words you have found. This could be done like this, if you are fine with modifying the words list:

text= 'the dog was there. the cat is there too. python is the best. the dog want want want was there. '

lst=[]
words=['dog', 'cat', 'chocolate']
for sentence in text.split('.'):
    sentence = sentence.strip()  # Remove whitespace around sentence
    for word in words:
        if word in sentence:
            print(sentence)
            lst.append(sentence) 
            # Remove the found word from words
            words.remove(word)
else:
    lst.append('na')
    print('na')

I also changed some variable names in order to make the code more easily readable. This piece of code outputs the following

the dog was there
the cat is there too
na

Answer 4

Shrinking your code down (just one for loop), you can use pop() on the word list to remove an item from there:

text = 'the dog was there. the cat is there too. python is the best. the dog want want want was there. '
sentences = text.split('.')
words=['dog', 'cat', 'chocolate']

for sentence in sentences:
    # Takes the first word as long as there are items in the list!
    word = words.pop(0) if words else None
    if word and word in sentence:
        print(sentence.strip())  # Removes whitespaces arround the sentence 
else:
    print('na')

Output:

the dog was there
the cat is there too
na