How to find index of an exact word in a string in Python

Question

word = 'laugh'    
string = 'This is laughing laugh'
index = string.find ( word )

index is 8, should be 17. I looked around hard, but could not find an answer.

Answer 1

You should use regex (with word boundary) as str.find returns the first occurrence. Then use the start attribute of the match object to get the starting index.

import re

string = 'This is laughing laugh'

a = re.search(r'\b(laugh)\b', string)
print(a.start())
>> 17

You can find more info on how it works here.

Answer 2

try this:

word = 'laugh'    
string = 'This is laughing laugh'.split(" ")
index = string.index(word)

This makes a list containing all the words and then searches for the relevant word. Then I guess you could add all of the lengths of the elements in the list less than index and find your index that way

position = 0
for i,word in enumerate(string):
    position += (1 + len(word))
    if i>=index:
        break

print position  

Hope this helps.

Answer 3

Here is one approach without regular expressions:

word = 'laugh'    
string = 'This is laughing laugh'
# we want to find this >>> -----
# index   0123456789012345678901     
words = string.split(' ')
word_index = words.index(word)
index = sum(len(x) + 1 for i, x in enumerate(words) 
            if i < word_index) 
=> 17

This splits the string into words, finds the index of the matching word and then sums up the lengths and the blank char as a separater of all words before it.

Update Another approach is the following one-liner:

index = string.center(len(string) + 2, ' ').find(word.center(len(word) + 2, ' '))

Here both the string and the word are right and left padded with blanks as to capture the full word in any position of the string.

You should of course use regular expressions for performance and convenience. The equivalent using the re module is as follows:

r = re.compile(r'\b%s\b' % word, re.I)
m = r.search(string)
index = m.start()

Here \b means word boundary, see the re documentation. Regex can be quite daunting. A great way to test and find regular expressions is using regex101.com

Answer 4

Strings in code are not separated by spaces. If you want to find the space, you must include the space in the word you are searching for. You may find it would actually be more efficient for you to split the string into words then iterate, e.g:

str = "This is a laughing laugh"
strList = str.split(" ")
for sWord in strList:
    if sWord == "laugh":
        DoStuff()

As you iterate you can add the length of the current word to an index and when you find the word, break from the loop. Don't forget to account for the spaces!

Answer 5

I stumbled upon this. I hope by now you would have figured it out. If you haven't maybe this would help. I had the same dilemma as you, was trying to print out a word using index.

string = 'This is laughing laugh'
word = string.split(" ")
print(word[02])

This would print out laughing.

I hope this helps. This is the first time of me answering a question on this forum, please pardon my syntax.

Thank you.