On Thu, 13 Jan 2005 11:40:52 -0800, Jeff Shannon <[EMAIL PROTECTED]> wrote:
>Bengt Richter wrote: > >> BTW, I'm sure you could write a generator that would take a file name >> and oldbinstring and newbinstring as arguments, and read and yield nice >> os-file-system-friendly disk-sector-multiple chunks, so you could write >> >> fout = open('mynewbinfile', 'wb') >> for buf in updated_file_stream('myoldbinfile','rb', oldbinstring, >> newbinstring): >> fout.write(buf) >> fout.close() > >What happens when the bytes to be replaced are broken across a block >boundary? ISTM that neither half would be recognized.... > >I believe that this requires either reading the entire file into >memory, to scan all at once, or else conditionally matching an >arbitrary fragment of the end of a block against the beginning of the >oldbinstring... Given that the file in question is only a few tens of >kbytes, I'd think that doing it in one gulp is simpler. (For a large >file, chunking it might be necessary, though...) > Might as well post this, in case you're interested... warning, not very tested. You want to write a proper test? ;-) ----< sreplace.py >------------------------------------------------- def sreplace(sseq, old, new, retsize=4096): """ iterate through sseq input string chunk sequence treating it as a continuous stream, replacing each substring old with new, and generating a sequence of retsize returned strings, except that the last may be shorter depedning on available input. """ inbuf = '' endsseq = False out = [] start = 0 lenold = len(old) lennew = len(new) while not endsseq: start, endprev = old and inbuf.find(old, start) or -1, start if start<0: start = endprev # restore find start pos for chunk in sseq: inbuf+= chunk; break else: out.append(inbuf[start:]) endsseq = True else: out.append(inbuf[endprev:start]) start += lenold out.append(new) if endsseq or sum(map(len, out))>=retsize: s = ''.join(out) while len(s)>= retsize: yield s[:retsize] s = s[retsize:] if endsseq: if s: yield s else: out = [s] if __name__ == '__main__': import sys args = sys.argv[:] usage = """ Test usage: [python] sreplace.py old new retsize [rest of args is string chunks for test] where old is old string to find in chunked stream and new is replacement and retsize is returned buffer size, except that last may be shorter""" if not args[1:]: raise SystemExit, usage try: args[3] = int(args[3]) args[0] = iter(sys.argv[4:]) print '%r\n-----------\n%s\n------------' %(sys.argv[1:], '\n'.join(sreplace(*args[:4]))) except Exception, e: print '%s: %s' %(e.__class__.__name__, e) raise SystemExit, usage -------------------------------------------------------------------- As mentioned, not tested very much beyond what you see: [ 2:43] C:\pywk\ut>py24 sreplace.py x _XX_ 20 This is x and abcxdef 012x345 zzxx zzz x ['x', '_XX_', '20', 'This', 'is', 'x', 'and', 'abcxdef', '012x345', 'zzxx', 'zzz', 'x'] ----------- Thisis_XX_andabc_XX_ def012_XX_345zz_XX__ XX_zzz_XX_ ------------ [ 2:43] C:\pywk\ut>py24 sreplace.py x _XX_ 80 This is x and abcxdef 012x345 zzxx zzz x ['x', '_XX_', '80', 'This', 'is', 'x', 'and', 'abcxdef', '012x345', 'zzxx', 'zzz', 'x'] ----------- Thisis_XX_andabc_XX_def012_XX_345zz_XX__XX_zzz_XX_ ------------ [ 2:43] C:\pywk\ut>py24 sreplace.py x _XX_ 4 This is x and abcxdef 012x345 zzxx zzz x ['x', '_XX_', '4', 'This', 'is', 'x', 'and', 'abcxdef', '012x345', 'zzxx', 'zzz', 'x'] ----------- This is_X X_an dabc _XX_ def0 12_X X_34 5zz_ XX__ XX_z zz_X X_ ------------ [ 2:44] C:\pywk\ut>py24 sreplace.py def DEF 80 This is x and abcxdef 012x345 zzxx zzz x ['def', 'DEF', '80', 'This', 'is', 'x', 'and', 'abcxdef', '012x345', 'zzxx', 'zzz', 'x'] ----------- ThisisxandabcxDEF012x345zzxxzzzx ------------ If you wanted to change a binary file, you'd use it something like (although probably let the default buffer size be at 4096, not 20, which is pretty silly other than demoing. At least the input chunks are 512 ;-) >>> from sreplace import sreplace >>> fw = open('sreplace.py.txt','wb') >>> for buf in sreplace(iter(lambda f=open('sreplace.py','rb'):f.read(512), >>> ''),'out','OUT',20): ... fw.write(buf) ... >>> fw.close() >>> ^Z [ 3:00] C:\pywk\ut>diff -u sreplace.py sreplace.py.txt --- sreplace.py Fri Jan 14 02:39:52 2005 +++ sreplace.py.txt Fri Jan 14 03:00:01 2005 @@ -7,7 +7,7 @@ """ inbuf = '' endsseq = False - out = [] + OUT = [] start = 0 lenold = len(old) lennew = len(new) @@ -17,21 +17,21 @@ start = endprev # restore find start pos for chunk in sseq: inbuf+= chunk; break else: - out.append(inbuf[start:]) + OUT.append(inbuf[start:]) endsseq = True else: - out.append(inbuf[endprev:start]) + OUT.append(inbuf[endprev:start]) start += lenold - out.append(new) - if endsseq or sum(map(len, out))>=retsize: - s = ''.join(out) + OUT.append(new) + if endsseq or sum(map(len, OUT))>=retsize: + s = ''.join(OUT) while len(s)>= retsize: yield s[:retsize] s = s[retsize:] if endsseq: if s: yield s else: - out = [s] + OUT = [s] if __name__ == '__main__': import sys Regards, Bengt Richter -- http://mail.python.org/mailman/listinfo/python-list