Which method would you use to determine whether a certain substring is present in a string?

I have a sub-string:

substring = "please help me out"

I have another string:

string = "please help me out so that I could solve this"

How do I find if substring is a subset of string using Python?

the Tin Man

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asked Sep 9, 2011 at 11:55

0

with in: substring in string:

>>> substring = "please help me out"
>>> string = "please help me out so that I could solve this"
>>> substring in string
True

answered Sep 9, 2011 at 11:57

MarcoSMarcoS

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5

foo = "blahblahblah"
bar = "somethingblahblahblahmeep"
if foo in bar:
    # do something

(By the way - try to not name a variable string, since there's a Python standard library with the same name. You might confuse people if you do that in a large project, so avoiding collisions like that is a good habit to get into.)

answered Sep 9, 2011 at 11:57

AmberAmber

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1

If you're looking for more than a True/False, you'd be best suited to use the re module, like:

import re
search="please help me out"
fullstring="please help me out so that I could solve this"
s = re.search(search,fullstring)
print(s.group())

s.group() will return the string "please help me out".

the Tin Man

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answered Nov 23, 2011 at 14:09

ewegesinewegesin

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People mentioned string.find(), string.index(), and string.indexOf() in the comments, and I summarize them here (according to the Python Documentation):

First of all there is not a string.indexOf() method. The link posted by Deviljho shows this is a JavaScript function.

Second the string.find() and string.index() actually return the index of a substring. The only difference is how they handle the substring not found situation: string.find() returns -1 while string.index() raises an ValueError.

answered Jan 19, 2015 at 20:40

Samuel LiSamuel Li

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Thought I would add this in case you are looking at how to do this for a technical interview where they don't want you to use Python's built-in function in or find, which is horrible, but does happen:

string = "Samantha"
word = "man"

def find_sub_string(word, string):
  len_word = len(word)  #returns 3

  for i in range(len(string)-1):
    if string[i: i + len_word] == word:
  return True

  else:
    return False

the Tin Man

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answered Mar 27, 2015 at 19:08

1

You can also try find() method. It determines if string str occurs in string, or in a substring of string.

str1 = "please help me out so that I could solve this"
str2 = "please help me out"
        
if (str1.find(str2)>=0):
  print("True")
else:
  print ("False")

Guy Avraham

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answered Sep 27, 2014 at 14:29

In [7]: substring = "please help me out"

In [8]: string = "please help me out so that I could solve this"

In [9]: substring in string
Out[9]: True

answered Sep 9, 2011 at 11:57

Fredrik PihlFredrik Pihl

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def find_substring():
    s = 'bobobnnnnbobmmmbosssbob'
    cnt = 0
    for i in range(len(s)):
        if s[i:i+3] == 'bob':
            cnt += 1
    print 'bob found: ' + str(cnt)
    return cnt

def main():
    print(find_substring())

main()

answered Jun 23, 2015 at 3:30

1

Can also use this method

if substring in string:
    print(string + '\n Yes located at:'.format(string.find(substring)))

answered Nov 21, 2016 at 15:38

jackotonyejackotonye

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Instead Of using find(), One of the easy way is the Use of 'in' as above.

if 'substring' is present in 'str' then if part will execute otherwise else part will execute.

answered May 7, 2018 at 11:42

Dcoder14Dcoder14

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