python 3.x - substitue string by index without using regular expressions -

it should easy, looking efficient way perform it.

i know split string 2 parts , insert new value, have tried substitute each line between indexes 22-26 follows:

line.replace(line[22:26],new_value)

the problem

however, function substitutes in line similar pattern in line[22:26].

in example below, want replace marked number 1 number 17:

here results. note replacement of 1 17 in several places:

thus don't understand behavior of replace command. there simple explanation of i'm doing wrong?

why don't want re

the values between index 22-26 not unified in form.

note: using python 3.5 on unix/linux machines.

str.replace replaces 1 sub-string pattern everywhere in string.

e.g.

'ab cd ab ab'.replace('ab', 'xy') # produces output 'xy cd xy xy' 

similarly,

mystr = 'ab cd ab ab' mystr.replace(mystr[0:2], 'xy') # produces output 'xy cd xy xy' 

what instead, replace just characters in position 22-26

line = line[0:22] + new_value + line[26:] 

also, looking @ data, seems me fixed-width text file. while suggestion work, more robust way process data read & separate different fields in record first, before processing data.

if have access pandas library, provides useful function reading fixed-width files