Unexpected break while reading a file in python

Question

I am trying to program a hex-viewer for cmd in python 2.7
It works almost fine, but if I try to view a compiled file on windows, it shows only a little part of it. I already figured out, that read() breaks at the first occurrence of 0x1a (in ASCII). Notepad++ shows this char as SUB. I don't know what this control-character does, why read() stops at this char and how to avoid this break. Can anyone help me?

Here's my whole code:

    def main():

        while True:
            print "Enter a file path:"
            path = raw_input()
            f = open(path, 'r')
            text = f.read() # seems to break at 0x1a/SUB
            f.close()
            for c in text:
                hex_c = hex(ord(c))[2:]
                if len(hex_c) % 2: # if the hex number consists of 1 digit
                    hex_c = '0' + hex_c # fill the string with a zero
                print hex_c,
            print # just as a line break in the console

    if __name__ == '__main__':

        main()

Jean-François Fabre · Accepted Answer · 2016-12-03 21:01:38Z

2

f = open(path, 'r') opens the file in text mode.

While it has little importance on Linux, if you stil use Python 2.x, on Windows, text mode enables end of line conversion (CRLF become LF aka \r\n become \n aka 0x0D 0x0A becomes 0x0A)

I must admit I cannot explain why you have this behaviour, but for a hex editor, you have open the file as binary or you'll lose all 0x0d bytes (and other surprises I'm apparently unaware of, I'll make some more research):

f = open(path, 'rb')

no conversion is performed, file is accessed in raw mode, I cannot see how it wouldn't fix your problem.

(also don't forget to f.close() your file, as it's currently not done, or use a with open(path,"rb") as f: statement.

BTW: direct 2-digit hex can be achieved by: hex_c = "%02x" % ord(c)

EDIT: I tried with python 3, and it won't even let me read a binary file as text. I got UnicodeDecodeError: 'charmap' codec can't decode byte 0x9d in position 46: character maps to <undefined>. At least you can't do it from the start!

edited Dec 3, 2016 at 21:01

answered Dec 3, 2016 at 20:46

Jean-François Fabre♦

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1 Comment

Aemyl Over a year ago

Thank you very much! I am actually closing the file directly after the read-call, I just forgot to type the code line here.

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