python - Replace all lines [fromString ,toString] in file -

i replace section of text in text file given string. example, given following file content:

1 ---from here--- 2 ---to here--- 3 

i write python function upon initiation in format of fashion :

replacesection('pathtofile','---from here---\n','---to here---\n','woo hoo!\n') 

this should change original file to:

1 woo hoo! 3 

i have come straightforward implementation (below) believe has disadvantages, , i'm wondering if there simpler implementation :

• the code long, makes understanding little cumbersome
• i iterate on code twice (instead of inplace replacements) - seems inefficient

• this same implementation use c++ code, , guess python has hidden beauties make implementation more elegant

  def replacesection(pathtofile,sectionopener,sectioncloser,replacewith = ''):     '''     delete lines in section of given file , put instead customized text.      return:     none if replacement performed , -1 otherwise.     '''     f = open(pathtofile,"r")     lines = f.readlines()     f.close()     if sectionopener in lines:         iswrite = true # while outside block , current line should kept         f = open(pathtofile,"w")         #write each line until reaching section opener         # write nothing until reaching section end.          line in lines :             if line == sectionopener:                 iswrite = false             if iswrite:             # outside undesired section , hence want keep current line                     f.write(line)             else:                 if line == sectioncloser:                     # it's last line of section                     f.write(replacewith)                     )                     iswrite = true                 else:                     # current line block wish delete                     # don't write it.                     pass         f.flush()         f.close()     else:         return -1 

here's itertools based approach:

from itertools import takewhile, dropwhile, chain, islice  open('input') fin, open('output', 'w') fout:     fout.writelines(chain(         takewhile(lambda l: l != '---from here---\n', fin),         ['woo hoo!\n'],         islice(dropwhile(lambda l: l != '---to here---\n', fin), 1, none)         )     ) 

so, until marker, write out original lines, line(s) want, then, ignore until end marker, , write remaining lines (skipping first it'll end marker)...