On Sat, May 19, 2018 at 8:33 PM, bartc <b...@freeuk.com> wrote: > On 19/05/2018 02:26, Chris Angelico wrote: >> >> On Sat, May 19, 2018 at 11:10 AM, bartc <b...@freeuk.com> wrote: > > >>> The .ppm (really .pbm) file which was the subject of this sub-thread has >>> its >>> header defined using ASCII. I don't think an EBCDIC 'P4' etc will work. >>> >> >> "Defined using ASCII" is a tricky concept. There are a number of file >> formats that have certain parts defined because of ASCII mnemonics, >> but are actually defined numerically. The PNG format begins with the >> four bytes 89 50 4E 47, chosen because three of those bytes represent >> the letters "PNG" in ASCII. But it's defined as those byte values. The >> first three represent "i&+" in EBCDIC, and that would be just as >> valid, because you get the correct bytes. >> >> Your file contains bytes. Not text. > > > Not you understand why some of us don't bother with 'text mode' files. > > However if you have an actual EBCDIC system and would to read .ppm files, > then you will have trouble reading the numeric parameters as they are > expressed using sequences of ASCII digits. > > The simplest way would be to pass each byte through an ASCII to EBCDIC > lookup table (so that code 0x37 for ASCII '7', which is EOT in EBCDIC, is > turned into 0xF8 which is EBCDIC '7'). > > But then you are acknowledging the file is, in fact, ASCII.
Cool! So what happens if you acknowledge that a file is ASCII, and then it starts with a byte value of E3 ? ChrisA -- https://mail.python.org/mailman/listinfo/python-list
