How to find all occurrences of a substring

Question

Python has string find   and string rfind   to get the index of a substring in a string   I m wondering whether there is something like string find all   which can return all found indexes  not only the first from the beginning or the first from the end    For example   string    test test test test   print string find  test     0 print string rfind  test     15   this is the goal print string find all  test      0 5 10 15

User · Accepted Answer

There is no simple built-in string function that does what you're looking for, but you could use the more powerful regular expressions:

import re
[m.start() for m in re.finditer('test', 'test test test test')]
#[0, 5, 10, 15]

If you want to find overlapping matches, lookahead will do that:

[m.start() for m in re.finditer('(?=tt)', 'ttt')]
#[0, 1]

If you want a reverse find-all without overlaps, you can combine positive and negative lookahead into an expression like this:

search = 'tt'
[m.start() for m in re.finditer('(?=%s)(?!.{1,%d}%s)' % (search, len(search)-1, search), 'ttt')]
#[1]

re.finditer returns a generator, so you could change the [] in the above to () to get a generator instead of a list which will be more efficient if you're only iterating through the results once.

User · Answer

gt  gt  gt  help str find  Help on method descriptor   find          S find sub   start   end    - gt  int   Thus  we can build it ourselves   def find all a str  sub       start   0     while True          start   a str find sub  start          if start    -1  return         yield start         start    len sub    use start    1 to find overlapping matches  list find all  spam spam spam spam    spam       0  5  10  15    No temporary strings or regexes required

User · Answer

def find index string  let       enumerated    place  for place  letter in enumerate string  if letter    let      return enumerated  for example   find index  quot hey doode find d quot    quot d quot     returns   4  7  13  15

User · Answer

this is an old thread but i got interested and wanted to share my solution   def find all a string  sub       result          k   0     while k  lt  len a string           k   a string find sub  k          if k    -1              return result         else              result append k              k    1  change to k    len sub  to not search overlapping results     return result   It should return a list of positions where the substring was found  Please comment if you see an error or room for improvment

User · Answer

If you re just looking for a single character  this would work   string    dooobiedoobiedoobie  match    o  reduce lambda count  char  count   1 if char    match else count  string  0    produces 7   Also   string    test test test test  match    test  len string split match   - 1   produces 4   My hunch is that neither of these  especially  2  is terribly performant

User · Answer

This does the trick for me using re finditer  import re  text    This is sample text to test if this pythonic            program can serve as an indexing platform for            finding words in a paragraph  It can give            values as to where the word is located with the            different examples as stated      find all occurances of the word  as  in the above text  find the word   re finditer  as   text   for match in find the word      print  start     end     search string                    format match start    match end    match group

User · Answer

This function does not look at all positions inside the string  it does not waste compute resources  My try   def findAll string word       all positions        next pos -1     while True          next pos string find word next pos 1          if next pos lt 0               break         all positions append next pos      return all positions   to use it call it like this   result findAll  this word is a big word man how many words are there    word

User · Answer

please look at below code     usr bin env python   coding utf-8      Python      def get substring indices text  s       result    i for i in range len text   if text startswith s  i       return result   if   name         main         text    How much wood would a wood chuck chuck if a wood chuck could chuck wood       s    wood      print get substring indices text  s

User · Answer

src   input     we will find substring in this string sub   input     substring  res      pos   src find sub  while pos    -1      res append pos      pos   src find sub  pos   1

User · Answer

You can easily use   string count  test      https   www programiz com python-programming methods string count  Cheers

User · Answer

This thread is a little old but this worked for me   numberString    onetwothreefourfivesixseveneightninefiveten  testString    five   marker   0 while marker  lt  len numberString       try          print numberString index  five  marker           marker   numberString index  five   marker    1     except ValueError          print  String not found           marker   len numberString

User · Answer

You can try     gt  gt  gt  string    test test test test   gt  gt  gt  for index value in enumerate string       if string index index  len  test         test           print index  0 5 10 15

User · Answer

When looking for a large amount of key words in a document  use flashtext  from flashtext import KeywordProcessor words     test    exam    quiz   txt    this is a test  kwp   KeywordProcessor   kwp add keywords from list words  result   kwp extract keywords txt  span info True    Flashtext runs faster than regex on large list of search words

User · Answer

By slicing we find all the combinations possible and append them in a list and find the number of times it occurs using count function  s input   n len s  l    f input   print s 0   for i in range 0 n       for j in range 1 n 1           l append s i j   if f in l      print l count f

User · Answer

You can use re finditer   for non-overlapping matches     gt  gt  gt  import re  gt  gt  gt  aString    this is a string where the substring  is  is repeated several times   gt  gt  gt  print   a start    a end    for a in list re finditer  is   aString      2  4    5  7    38  40    42  44     but won t work for   In  1   aString  ababa   In  2   print   a start    a end    for a in list re finditer  aba   aString    Output    0  3

User · Answer

Again  old thread  but here s my solution using a generator and plain str find    def findall p  s          Yields all the positions of     the pattern p in the string s         i   s find p      while i    -1          yield i         i   s find p  i 1    Example  x    banananassantana    i  x i i 2   for i in findall  na   x     returns    2   na     4   na     6   na     14   na

User · Answer

Come  let us recurse together   def locations of substring string  substring          Return a list of locations of a substring          substring length   len substring          def recurse locations found  start           location   string find substring  start          if location    -1              return recurse locations found    location   location substring length          else              return locations found      return recurse     0   print locations of substring  this is a test for finding this and this    this      prints  0  27  36    No need for regular expressions this way

User · Answer

This is solution of a similar question from hackerrank  I hope this could help you   import re a   input   b   input   if b not in a      print  -1 -1   else       create two list as     start indc    m start   for m in re finditer         b        a       for i in range len start indc            print  start indc i   start indc i  len b -1     Output     aaadaa aa  0  1   1  2   4  5

User · Answer

The pythonic way would be   mystring    Hello World  this should work   find all   lambda c s   x for x in range c find s   len c   if c x     s     s represents the search string   c represents the character string  find all mystring  o        will return all positions of  o    4  7  20  26    gt  gt  gt

User · Answer

Whatever the solutions provided by others are completely based on the available method find   or any available methods      What is the core basic algorithm to find all the occurrences of a   substring in a string    def find all string substring               Function  Returning all the index of substring in a string     Arguments  String and the search string     Return Returning a list             length   len substring      c 0     indexes          while c  lt  len string           if string c c length     substring              indexes append c          c c 1     return indexes      You can also inherit str class to new class and can use this function   below    class newstr str   def find all string substring               Function  Returning all the index of substring in a string     Arguments  String and the search string     Return Returning a list             length   len substring      c 0     indexes          while c  lt  len string           if string c c length     substring              indexes append c          c c 1     return indexes   Calling the method     newstr find all  Do you find this answer helpful  then upvote   this    this

User · Answer

Here s a  very inefficient  way to get all  i e  even overlapping  matches    gt  gt  gt  string    test test test test   gt  gt  gt   i for i in range len string   if string startswith  test   i    0  5  10  15

[python] How to find all occurrences of a substring?

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