Find string between two substrings

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How do I find a string between two substrings ('123STRINGabc' -> 'STRING')?

My current method is like this:

>>> start = 'asdf=5;'
>>> end = '123jasd'
>>> s = 'asdf=5;iwantthis123jasd'
>>> print((s.split(start))[1].split(end)[0])
iwantthis

However, this seems very inefficient and un-pythonic. What is a better way to do something like this?

Forgot to mention:
The string might not start and end with start and end. They may have more characters before and after.

Contents hide
Answers:
Method 1
Method 2
Method 3
Method 4
Method 5
Method 6
Method 7
Method 8
Method 9
Method 10
Method 11
Method 12
Method 13
Method 14
Method 15
Method 16
Method 17
Method 18
Method 19
Method 20

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

import re

s = 'asdf=5;iwantthis123jasd'
result = re.search('asdf=5;(.*)123jasd', s)
print(result.group(1))

Method 2

s = "123123STRINGabcabc"

def find_between( s, first, last ):
    try:
        start = s.index( first ) + len( first )
        end = s.index( last, start )
        return s[start:end]
    except ValueError:
        return ""

def find_between_r( s, first, last ):
    try:
        start = s.rindex( first ) + len( first )
        end = s.rindex( last, start )
        return s[start:end]
    except ValueError:
        return ""


print find_between( s, "123", "abc" )
print find_between_r( s, "123", "abc" )

gives:

123STRING
STRINGabc

I thought it should be noted – depending on what behavior you need, you can mix index and rindex calls or go with one of the above versions (it’s equivalent of regex (.*) and (.*?) groups).

Method 3

start = 'asdf=5;'
end = '123jasd'
s = 'asdf=5;iwantthis123jasd'
print s[s.find(start)+len(start):s.rfind(end)]

gives 

iwantthis

Method 4

s[len(start):-len(end)]

Method 5

String formatting adds some flexibility to what Nikolaus Gradwohl suggested. start and end can now be amended as desired.

import re

s = 'asdf=5;iwantthis123jasd'
start = 'asdf=5;'
end = '123jasd'

result = re.search('%s(.*)%s' % (start, end), s).group(1)
print(result)

Method 6

If you don’t want to import anything, try the string method .index():

text = 'I want to find a string between two substrings'
left = 'find a '
right = 'between two'

# Output: 'string'
print(text[text.index(left)+len(left):text.index(right)])

Method 7

Just converting the OP’s own solution into an answer:

def find_between(s, start, end):
    return (s.split(start))[1].split(end)[0]

Method 8

source='your token <a href="https://getridbug.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="e7b88f829582d7a78381">[email protected]</a> and maybe <a href="https://getridbug.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="edb285889f88dcad898b">[email protected]</a> or maybe <a href="https://getridbug.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="530c3b36213661133735">[email protected]</a>'
start_sep='_'
end_sep='@df'
result=[]
tmp=source.split(start_sep)
for par in tmp:
  if end_sep in par:
    result.append(par.split(end_sep)[0])

print result

must show:
here0, here1, here2

the regex is better but it will require additional lib an you may want to go for python only

Method 9

Here is one way to do it

_,_,rest = s.partition(start)
result,_,_ = rest.partition(end)
print result

Another way using regexp

import re
print re.findall(re.escape(start)+"(.*)"+re.escape(end),s)[0]

or

print re.search(re.escape(start)+"(.*)"+re.escape(end),s).group(1)

Method 10

Here is a function I did to return a list with a string(s) inbetween string1 and string2 searched.

def GetListOfSubstrings(stringSubject,string1,string2):
    MyList = []
    intstart=0
    strlength=len(stringSubject)
    continueloop = 1

    while(intstart < strlength and continueloop == 1):
        intindex1=stringSubject.find(string1,intstart)
        if(intindex1 != -1): #The substring was found, lets proceed
            intindex1 = intindex1+len(string1)
            intindex2 = stringSubject.find(string2,intindex1)
            if(intindex2 != -1):
                subsequence=stringSubject[intindex1:intindex2]
                MyList.append(subsequence)
                intstart=intindex2+len(string2)
            else:
                continueloop=0
        else:
            continueloop=0
    return MyList


#Usage Example
mystring="s123y123o123pp123y6"
List = GetListOfSubstrings(mystring,"1","y68")
for x in range(0, len(List)):
               print(List[x])
output:


mystring="s123y123o123pp123y6"
List = GetListOfSubstrings(mystring,"1","3")
for x in range(0, len(List)):
              print(List[x])
output:
    2
    2
    2
    2

mystring="s123y123o123pp123y6"
List = GetListOfSubstrings(mystring,"1","y")
for x in range(0, len(List)):
               print(List[x])
output:
23
23o123pp123

Method 11

To extract STRING, try:

myString = '123STRINGabc'
startString = '123'
endString = 'abc'

mySubString=myString[myString.find(startString)+len(startString):myString.find(endString)]

Method 12

You can simply use this code or copy the function below. All neatly in one line.

def substring(whole, sub1, sub2):
    return whole[whole.index(sub1) : whole.index(sub2)]

If you run the function as follows.

print(substring("5+(5*2)+2", "(", "("))

You will pobably be left with the output:

(5*2

rather than

5*2

If you want to have the sub-strings on the end of the output the code must look like below.

return whole[whole.index(sub1) : whole.index(sub2) + 1]

But if you don’t want the substrings on the end the +1 must be on the first value.

return whole[whole.index(sub1) + 1 : whole.index(sub2)]

Method 13

These solutions assume the start string and final string are different. Here is a solution I use for an entire file when the initial and final indicators are the same, assuming the entire file is read using readlines():

def extractstring(line,flag='$'):
    if flag in line: # $ is the flag
        dex1=line.index(flag)
        subline=line[dex1+1:-1] #leave out flag (+1) to end of line
        dex2=subline.index(flag)
        string=subline[0:dex2].strip() #does not include last flag, strip whitespace
    return(string)

Example:

lines=['asdf 1qr3 qtqay 45q at $A NEWT?$ asdfa afeasd',
    'afafoaltat $I GOT BETTER!$ derpity derp derp']
for line in lines:
    string=extractstring(line,flag='$')
    print(string)

Gives:

A NEWT?
I GOT BETTER!

Method 14

This is essentially cji’s answer – Jul 30 ’10 at 5:58.
I changed the try except structure for a little more clarity on what was causing the exception.

def find_between( inputStr, firstSubstr, lastSubstr ):
'''
find between firstSubstr and lastSubstr in inputStr  STARTING FROM THE LEFT
    http://stackoverflow.com/questions/3368969/find-string-between-two-substrings
        above also has a func that does this FROM THE RIGHT   
'''
start, end = (-1,-1)
try:
    start = inputStr.index( firstSubstr ) + len( firstSubstr )
except ValueError:
    print '    ValueError: ',
    print "firstSubstr=%s  -  "%( firstSubstr ), 
    print sys.exc_info()[1]

try:
    end = inputStr.index( lastSubstr, start )       
except ValueError:
    print '    ValueError: ',
    print "lastSubstr=%s  -  "%( lastSubstr ), 
    print sys.exc_info()[1]

return inputStr[start:end]

Method 15

from timeit import timeit
from re import search, DOTALL


def partition_find(string, start, end):
    return string.partition(start)[2].rpartition(end)[0]


def re_find(string, start, end):
    # applying re.escape to start and end would be safer
    return search(start + '(.*)' + end, string, DOTALL).group(1)


def index_find(string, start, end):
    return string[string.find(start) + len(start):string.rfind(end)]


# The wikitext of "Alan Turing law" article form English Wikipeida
# https://en.wikipedia.org/w/index.php?title=Alan_Turing_law&action=edit&oldid=763725886
string = """..."""
start = '==Proposals=='
end = '==Rival bills=='

assert index_find(string, start, end) 
       == partition_find(string, start, end) 
       == re_find(string, start, end)

print('index_find', timeit(
    'index_find(string, start, end)',
    globals=globals(),
    number=100_000,
))

print('partition_find', timeit(
    'partition_find(string, start, end)',
    globals=globals(),
    number=100_000,
))

print('re_find', timeit(
    're_find(string, start, end)',
    globals=globals(),
    number=100_000,
))

Result:

index_find 0.35047444528454114
partition_find 0.5327825636197754
re_find 7.552149639286381

re_find was almost 20 times slower than index_find in this example.

Method 16

My method will be to do something like,

find index of start string in s => i
find index of end string in s => j

substring = substring(i+len(start) to j-1)

Method 17

This I posted before as code snippet in Daniweb:

# picking up piece of string between separators
# function using partition, like partition, but drops the separators
def between(left,right,s):
    before,_,a = s.partition(left)
    a,_,after = a.partition(right)
    return before,a,after

s = "bla bla blaa <a>data</a> lsdjfasdjöf (important notice) 'Daniweb forum' tcha tcha tchaa"
print between('<a>','</a>',s)
print between('(',')',s)
print between("'","'",s)

""" Output:
('bla bla blaa ', 'data', " lsdjfasdjxc3xb6f (important notice) 'Daniweb forum' tcha tcha tchaa")
('bla bla blaa <a>data</a> lsdjfasdjxc3xb6f ', 'important notice', " 'Daniweb forum' tcha tcha tchaa")
('bla bla blaa <a>data</a> lsdjfasdjxc3xb6f (important notice) ', 'Daniweb forum', ' tcha tcha tchaa')
"""

Method 18

Parsing text with delimiters from different email platforms posed a larger-sized version of this problem. They generally have a START and a STOP. Delimiter characters for wildcards kept choking regex. The problem with split is mentioned here & elsewhere – oops, delimiter character gone. It occurred to me to use replace() to give split() something else to consume. Chunk of code:

nuke = '~~~'
start = '|*'
stop = '*|'
julien = (textIn.replace(start,nuke + start).replace(stop,stop + nuke).split(nuke))
keep = [chunk for chunk in julien if start in chunk and stop in chunk]
logging.info('keep: %s',keep)

Method 19

Further from Nikolaus Gradwohl answer, I needed to get version number (i.e., 0.0.2) between(‘ui:’ and ‘-‘) from below file content (filename: docker-compose.yml):

    version: '3.1'
services:
  ui:
    image: repo-pkg.dev.io:21/website/ui:0.0.2-QA1
    #network_mode: host
    ports:
      - 443:9999
    ulimits:
      nofile:test

and this is how it worked for me (python script):

import re, sys

f = open('docker-compose.yml', 'r')
lines = f.read()
result = re.search('ui:(.*)-', lines)
print result.group(1)


Result:
0.0.2

Method 20

This seems much more straight forward to me:

import re

s = 'asdf=5;iwantthis123jasd'
x= re.search('iwantthis',s)
print(s[x.start():x.end()])


All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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