Examples for string find in Python

Question

I am trying to find some examples but no luck. Does anyone know of some examples on the net? I would like to know what it returns when it can't find, and how to specify from start to end, which I guess is going to be 0, -1.

Are you asking about http://docs.python.org/library/stdtypes.html#id4 ? Are you asking about the find method, specifically? http://docs.python.org/library/stdtypes.html#str.find — S.Lott, Mar 23 '09 at 19:00
Thanks yeah just the find method. I found that page but no examples. — Joan Venge, Mar 23 '09 at 19:03

score 113 · Answer 1 · answered Mar 23 '09 at 19:00

113

I'm not sure what you're looking for, do you mean find()?

>>> x = "Hello World"
>>> x.find('World')
6
>>> x.find('Aloha');
-1

answered Mar 23 '09 at 19:00

Paolo Bergantino

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1

Thanks, what do you get, if it can't find? – Joan Venge Mar 23 '09 at 19:00
2

Thanks, but why -1 here, not for index? I thought python prefers exceptions over special return values. – Joan Venge Mar 23 '09 at 19:02
Thanks SilentGhost, I used your method. – Joan Venge Mar 23 '09 at 19:04
2

find and index are the same functionality but with different results on no match. Python might in general prefer exceptions, but many users expect there to be a non-exception-raising-find-index method as well, especially as that's how it's done in almost every other language. – bobince Mar 23 '09 at 19:35
this works great for me - totally forgot that 0 result actually means a match! – Gordon Oct 07 '16 at 14:49
can we use or here for ex- x.find("Welcome" or "welcome") – Pooja Khatri Mar 23 '20 at 11:55

score 45 · Accepted Answer · answered Mar 23 '09 at 19:00

45

you can use str.index too:

>>> 'sdfasdf'.index('cc')
Traceback (most recent call last):
  File "<pyshell#144>", line 1, in <module>
    'sdfasdf'.index('cc')
ValueError: substring not found
>>> 'sdfasdf'.index('df')
1

answered Mar 23 '09 at 19:00

SilentGhost

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Why would you choose one over the other? – endolith Nov 08 '09 at 01:46
1

it raises the error instead of returning a code, which is more pythonic, in my opinion. – SilentGhost Nov 08 '09 at 11:33
7

exceptions should not be used for flow control. so, only use index() if no match would be abnormal. – aehlke Jul 05 '10 at 11:19
10

@Wahnfrieden: using exception is perfectly pythonic. And certainly doesn't deserve a downvote. – SilentGhost Jul 05 '10 at 12:44
8

@aehlke in fact, in Python, using exceptions to control flow is usual and even recommended: http://stackoverflow.com/questions/6092992/why-is-it-easier-to-ask-forgiveness-than-permission-in-python-but-not-in-java – Rafael Almeida Jan 09 '12 at 20:32

score 32 · Answer 3 · edited Oct 04 '19 at 13:16

From the documentation:

str.find(sub[, start[, end]])
Return the lowest index in the string where substring sub is found within the slice s[start:end]. Optional arguments start and end are interpreted as in slice notation. Return -1 if sub is not found.

So, some examples:

>>> my_str = 'abcdefioshgoihgs sijsiojs '
>>> my_str.find('a')
0
>>> my_str.find('g')
10
>>> my_str.find('s', 11)
15
>>> my_str.find('s', 15)
15
>>> my_str.find('s', 16)
17
>>> my_str.find('s', 11, 14)
-1

score 17 · Answer 4 · answered Mar 23 '09 at 19:02

17

Honestly, this is the sort of situation where I just open up Python on the command line and start messing around:

 >>> x = "Dana Larose is playing with find()"
 >>> x.find("Dana")
 0
 >>> x.find("ana")
 1
 >>> x.find("La")
 5
 >>> x.find("La", 6)
 -1

Python's interpreter makes this sort of experimentation easy. (Same goes for other languages with a similar interpreter)

answered Mar 23 '09 at 19:02

Dana

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IPython makes this sort of thing even better. – endolith Nov 08 '09 at 01:45

score 6 · Answer 5 · answered Sep 04 '12 at 06:44

6

If you want to search for the last instance of a string in a text, you can run rfind.

Example:

   s="Hello"
   print s.rfind('l')

output: 3

*no import needed

Complete syntax:

stringEx.rfind(substr, beg=0, end=len(stringEx))

answered Sep 04 '12 at 06:44

LucianNovo

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score 2 · Answer 6 · answered Mar 23 '09 at 19:01

find( sub[, start[, end]])

Return the lowest index in the string where substring sub is found, such that sub is contained in the range [start, end]. Optional arguments start and end are interpreted as in slice notation. Return -1 if sub is not found.

From the docs.

score 1 · Answer 7 · edited Sep 30 '20 at 19:16

1

Try

myString = 'abcabc'
myString.find('a')

This will give you the index!!!

edited Sep 30 '20 at 19:16

Exelian

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answered Sep 30 '20 at 18:39

Dave Brown

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Hi @Dave Brown, did you test your code? I think you'll find that it doesn't perform as indented because you made a typo – Exelian Sep 30 '20 at 19:15

score 0 · Answer 8 · answered Sep 28 '13 at 06:11

Try this:

with open(file_dmp_path, 'rb') as file:
fsize = bsize = os.path.getsize(file_dmp_path)
word_len = len(SEARCH_WORD)
while True:
    p = file.read(bsize).find(SEARCH_WORD)
    if p > -1:
        pos_dec = file.tell() - (bsize - p)
        file.seek(pos_dec + word_len)
        bsize = fsize - file.tell()
    if file.tell() < fsize:
        seek = file.tell() - word_len + 1
        file.seek(seek)
    else:
        break

score 0 · Answer 9 · answered Feb 04 '18 at 17:29

0

if x is a string and you search for y which also a string their is two cases : case 1: y is exist in x so x.find(y) = the index (the position) of the y in x . case 2: y is not exist so x.find (y) = -1 this mean y is not found in x.

answered Feb 04 '18 at 17:29

N.Elsayed

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Examples for string find in Python

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