what does := means simply?
MRAB
python at mrabarnett.plus.com
Sat May 19 15:07:53 EDT 2018
On 2018-05-19 13:28, bartc wrote:
> On 19/05/2018 12:38, Chris Angelico wrote:
>> On Sat, May 19, 2018 at 8:33 PM, bartc <bc at freeuk.com> wrote:
>
>>> 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 ?
>
> It depends.
>
> If this is a .ppm file I'm trying to read, and it starts with anything
> other than 'P' followed by one of '1','2','3','4','5','6' (by which I
> mean the ASCII codes for those), then it's a bad ppm file.
>
> What are you really trying to say here?
>
> Out of interest, how would Python handle the headers for binary file
> formats P4, P5, P6? I'd have a go but I don't want to waste half the day
> trying to get past the language.
>
> It is quite possible to deal with files, including files which are
> completely or partially text, a byte at a time, without having silly
> restrictions put on them by the language.
>
> Here's the palaver I had to go through last time I wrote such a file
> using Python, and this is just for the header:
>
> s="P6\n%d %d\n255\n" % (hdr.width, hdr.height)
> sbytes=array.array('B',list(map(ord,s)))
> f.write(sbytes)
>
> Was there a simple way to write way to do this? Most likely, but you
> have to find it first! Here's how I write it elsewhere:
>
> println @f, "P6"
> println @f, width,height
> println @f, 255
>
> It's simpler because it doesn't get tied up in knots in trying to make
> text different from bytes, bytearrays or array.arrays.
>
It's very simple:
s = b"P6\n%d %d\n255\n" % (hdr.width, hdr.height)
f.write(s)
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