error writing str to binary stream - fails in Python 3.0.1, works in 2.x

wallenpb at wallenpb at
Mon Mar 16 22:31:41 CET 2009

On Mar 16, 4:10 pm, Benjamin Peterson <benja... at> wrote:
>  <wallenpb <at>> writes:
> > self.out.write(b'BM') worked beautifully.  Now I also have a similar
> > issue, for instance:
> > self.out.write("%c" % y) is also giving me the same error as the other
> > statement did.
> > I tried self.out.write(bytes("%c" %y),encoding=utf-8) in an attempt to
> > convert to bytes, which it did, but not binary.  How do I affect
> > self.out.write("%c" % y) to write out as a binary byte steam?  I also
> > tried self.out.write(b"%c" % y), but b was an illegal operator in when
> > used that way.
> > It is also supposed to be data being written to the .bmp file. --Bill
> Are you writing to sys.stdout? If so, use sys.stdout.buffer.write(b'some
> bytes'). If you're writing to a file, you have to open it in binary mode like
> this: open("someimage.bmp", "wb")

Yes, I am writing to a file.  That portion is correct and goes like
    self.out.write(b"BM")          # This line works thanks to advice
given in previous reply

However, here is some more code that is not working and the error it
def write_int(self,n):
    str_out='%c%c%c%c' % ((n&255),(n>>8)&255,(n>>16)&255,(n>>24)&255)
    self.out.write(str_out)   #this is line 29, does not work - not
sure how to get this complex str converted over to binary bytes to
write to bmp file.
                              #tried to use self.out.write(bytes
("blah", encoding='utf-8')) type coding here.  This way ran without
error, but
                              #did not write proper data to the .bmp
file.In hex editor it was obvious it was filling in wrong bits.
                              #Also tried self.out.write(b'%c%c%c%c' %
(blah)) but this gave errors for bad operands for % operator.
Traceback (most recent call last):
    File "C:\Python30\", line 29, in write_int
  File "C:\Python30\lib\", line 1038, in write
    raise TypeError("can't write str to binary stream")
TypeError: can't write str to binary stream

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