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.

Solution 1

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

Solution 2

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

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

Solution 3

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

Solution 4

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)

Solution 5

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))

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Comments

[Joan Venge]

Thanks, what do you get, if it can't find?

[Joan Venge]

Thanks, but why -1 here, not for index? I thought python prefers exceptions over special return values.

[Joan Venge]

Thanks SilentGhost, I used your method.

[Amit Patil]

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.

[endolith]

IPython makes this sort of thing even better.

[endolith]

Why would you choose one over the other?

[SilentGhost]

it raises the error instead of returning a code, which is more pythonic, in my opinion.

[Asela Liyanage]

exceptions should not be used for flow control. so, only use index() if no match would be abnormal.

[SilentGhost]

@Wahnfrieden: using exception is perfectly pythonic. And certainly doesn't deserve a downvote.

[Rafael Almeida]

@aehlke in fact, in Python, using exceptions to control flow is usual and even recommended: stackoverflow.com/questions/6092992/…

[Gordon]

this works great for me - totally forgot that 0 result actually means a match!

[Pooja Khatri]

can we use or here for ex- x.find("Welcome" or "welcome")

[Exelian]

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