Insert some string into given string at given index in Python

Question

I am newbie in Python facing a problem  How to insert some fields in already existing string   For example  suppose I have read one line from any file which contains   line    Name Age Group Class Profession    Now I have to insert 3rd Field Group  3 times more in the same line before Class field  It means the output line should be    output line    Name Age Group Group Group Group Class Profession    I can retrieve 3rd field easily  using split method   but please let me know the easiest way of inserting into the string

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Answer for Insert characters of string in other string al located positions  str1    ibuprofen  str2    MEDICAL  final string    Value   2 list2    result  str1 i i Value  for i in range 0  len str1   Value   count   0  for letter in result      if count  lt  len result -1          final string   letter   str2 count          list2 append final string      elif   len result -1   count           list2 append letter   str2 count len str2            break     count    1  print    join list2

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Implementation  The functions below will allow one to insert one string into another string   def str insert from me  into me  at               Inserts the string  lt from me gt  into  lt into me gt       Input  lt at gt  must be an integer index of  lt into me gt  or a substring of  lt into me gt       Inserts  lt from me gt  AFTER  lt at gt   not before  lt at gt       Inputs  lt from me gt  and  lt into me gt  must have working   str   methods defined      This is satisfied if they already are strings       If not already strings   lt from me gt    lt into me gt  are converted into strings       If you try to insert an empty string  that s fine  and the result     is no different from the original       In order to insert  from me  after nothing  insert at the beginning of the string  use          at       or  at   0             try          return str insert or raise from me  into me  at      except ValueError as err          serr   str err          if  str insert or raise   name   in serr  and  not found  in serr and   lt at gt   in serr                if can t find where to insert stuff  don t bother to insert it               use str insert or raise if you want an exception instead             return into me         else              raise err                                                                  def str insert or raise from me  into me  at               Inserts the string  lt from me gt  into  lt into me gt       Inserts  lt from me gt  AFTER  lt at gt   not before  lt at gt       Input  lt at gt  must be an integer index of  lt into me gt  or a substring of  lt into me gt       If  lt at gt  is the string  15   that substring will be searched for       15  will not be interpreted as an index subscript               Inputs  lt from me gt  and  lt into me gt  must have working   str   methods defined      If not already strings   lt from me gt    lt into me gt  are converted into strings        If you try to insert something  but we cannot find the position where     you said to insert it  then an exception is thrown guaranteed to at least     contain the following three substrings          str insert or raise   name            not found            lt at gt               try          if isinstance at  int               return str insert by int from me  into me  at            Below  the calls to str   work fine if  lt at gt  and  lt from me gt  are already strings           it makes them strings if they are not already         return str insert by str str from me   str into me   str at       except ValueError as err          serr   str err          if  empty string  in serr              return into me   We allow insertion of the empty string         elif    lt at gt   in serr  and  not found  in serr              msg start    In     str insert or raise   name                       msg    msg start    ninput      lt at gt  string     not found in      lt into me gt                                    ninput  lt      str at       gt  not found in  lt    str into me     gt                msg      join msg              raise ValueError msg  from None         else             raise err                                                               def str insert by str from me  into me  at               Inserts the string  lt from me gt  into  lt into me gt       puts  from me  AFTER  at   not before  at      For example          str insert or raise at    2    from me    0   into me    123       puts the zero after the 2  not before the 2     The call returns  1203  not  1023       Throws exceptions if input arguments are not strings       Also  if  lt from me gt  is empty or  lt at gt  is not a substring of  lt into me gt  then     an exception is raised       For fewer exceptions  use  lt str insert or raise gt  instead              try          s   into me replace at  at   from me  1      except TypeError as terr    inputs to replace are not strings         msg list     Inputs to function    str insert by str   name        must be strings           raise TypeError    join msg list   from None       At the end of call to replace    the  1   indicates we will replace       the leftmost occurrence of  lt at gt   instead of every occurrence of  lt at gt      if  s    into me      lt at gt  string not found and or  lt from me gt  is the empty string         msg start    In     str insert by str   name                   if from me                    msg      join  msg start   attempted to insert an empty string                raise ValueError msg  from None         raise ValueError msg start   Input  lt at gt  string not found in  lt into me gt                                           nUnable to determine where you want the substring inserted    from None     return s                                                    def str insert by int from me  into me  at                 Inserts the string  lt from me gt  into  lt into me gt  at integer index  lt at gt            throws exceptions if input arguments are not strings            Also  throws an  exception if you try to insert the empty string           If  lt at gt  is less than zero   lt from me gt  gets placed at the       beginning of  lt into me gt            If  lt at gt  is greater than the largest index of  lt into me gt          lt from me gt  gets placed after the end of  lt into me gt       For fewer exceptions  use  lt str insert or raise gt  instead              at   into me   at if at  gt  0 else 0       return str insert by str from me  into me  at    Usage  The code below demonstrates how to call the str insert function given earlier      def foo  args       return args  F    F     s    Using the string   John    to specify where to make the insertion  result   str insert from me   F  into me   John Kennedy   at   John    print foo   n n   s    n   result    s    Using an int returned by find   Ken    to specify where to make the insertion  index    John Kennedy  find  Ken     returns the position of the first letter of  Ken   not the last letter result   str insert from me   F  into me   John Kennedy   at   index  print foo   n n   s    n   result    s    Using an int  5  to specify where to make the insertion   result   str insert from me   F  into me   John Kennedy   at   5  print foo   n n   s    n   result    s    Looking for an  at  string which does not exist  result   str insert from me   F  into me   John Kennedy   at   x   print foo   n n   s    n   result    s      join   Looking for the empty string                   nFind one immediately at the beginning of the string    result   str insert from me   F  into me   John Kennedy   at       print foo   n n   s    n   result    s    Insert an empty string at index 3  No visible change  result   str insert from me       into me    John Kennedy   at   3  print foo   n n   s    n   result        for index in  -5  -1  0  1  997  999       s    index     str index      result   str insert from me   F  into me    John Kennedy   at   index      print foo   n n   s    n   result     Warning About Lack of Ability to Modify In-Place  None of the functions above will modify a string  in-place   The functions each return a modified copy of the string  but the original string  remains intact   For example   s      join   Below is what we get when we forget                  to overwrite the string with the value                  returned by str insert or raise      examp str    John Kennedy  str insert  John    F  examp str  print foo   n n   s    n   examp str      examp str is still  John Kennedy  without the F

User · Answer

I know it s malapropos  but IMHO easy way is   def insert  source str  insert str  pos       return source str  pos  insert str source str pos

User · Answer

For the sake of future  newbies  tackling this problem  I think a quick answer would be fitting to this thread   Like bgporter said  Python strings are immutable  and so  in order to modify a string you have to make use of the pieces you already have   In the following example I insert  Fu  in to  Kong Panda   to create  Kong Fu Panda    gt  gt  gt  line    Kong Panda   gt  gt  gt  index   line find  Panda    gt  gt  gt  output line   line  index     Fu     line index    gt  gt  gt  output line  Kong Fu Panda    In the example above  I used the index value to  slice  the string in to 2 substrings  1 containing the substring before the insertion index  and the other containing the rest  Then I simply add the desired string between the two and voil    we have inserted a string inside another   Python s slice notation has a great answer explaining the subject of string slicing

User · Answer

I had a similar problem for my DNA assignment and I used bgporter s advice to answer it  Here is my function which creates a new string     def insert sequence str1  str2  int            str1  str2  int  - gt  str      Return the DNA sequence obtained by inserting the      second DNA sequence into the first DNA sequence      at the given index        gt  gt  gt  insert sequence  CCGG    AT   2      CCATGG      gt  gt  gt  insert sequence  CCGG    AT   3      CCGATG      gt  gt  gt  insert sequence  CCGG    AT   4      CCGGAT      gt  gt  gt  insert sequence  CCGG    AT   0      ATCCGG      gt  gt  gt  insert sequence  CCGGAATTGG    AT   6      CCGGAAATTTGG               str1 split1   str1  int      str1 split2   str1 int       new string   str1 split1   str2   str1 split2     return new string

User · Answer

line  Name Age Group Class Profession  arr   line split   for i in range 3       arr insert 2  arr 2   print     join arr

User · Answer

An important point that often bites new Python programmers but the other posters haven t made explicit is that strings in Python are immutable -- you can t ever modify them in place    You need to retrain yourself when working with strings in Python so that instead of thinking   How can I modify this string   instead you re thinking  how can I create a new string that has some pieces from this one I ve already gotten

User · Answer

There are several ways to do this   One way is to use slicing    gt  gt  gt  a  line Name Age Group Class Profession   gt  gt  gt  b a split    gt  gt  gt  b 2 2   b 2   3  gt  gt  gt  b   line Name    Age    Group    Group    Group    Group    Class    Profession    gt  gt  gt  a     join b   gt  gt  gt  a  line Name Age Group Group Group Group Class Profession    Another would be to use regular expressions    gt  gt  gt  import re  gt  gt  gt  a re sub r   S  s  S  s    S  s         r  1 2 2 2 2 3   a   gt  gt  gt  a  line Name Age Group Group Group Group Class Profession

[python] Insert some string into given string at given index in Python

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