Kurt Mueller wrote:
> Am 29.08.2013 11:12, schrieb Peter Otten:
>> kurt.alfred.muel...@gmail.com wrote:
>>> On Wednesday, August 28, 2013 1:13:36 PM UTC+2, Dave Angel wrote:
>>>> On 28/8/2013 04:32, Kurt Mueller wrote:
>>>>> For some text manipulation tasks I need a template to split lines
>>>>> from stdin into a list of strings the way shlex.split() does it.
>>>>> The encoding of the input can vary.
>
>> You can compromise and read ahead a limited number of lines. Here's my
>> demo script (The interesting part is detect_encoding(), I got a bit
>> distracted by unrelated stuff...). The script does one extra
>> decode/encode cycle -- it should be easy to avoid that if you run into
>> performance issues.
>
> I took your script as a template.
> But I used the libmagic library (pyhton-magic) instead of chardet.
> See http://linux.die.net/man/3/libmagic
> and https://github.com/ahupp/python-magic
> ( I made tests with files of different size, up to 1.2 [GB] )
>
> I had following issues:
>
> - I a real file, the encoding was detected as 'ascii' for
> detect_lines=1000.
> In line 1002 there was an umlaut character. So then the
> line.decode(encoding) failed. I think to add the errors parameter,
> line.decode(encoding, errors='replace')
Tough luck ;) You could try and tackle the problem by skipping leading
ascii-only lines. Untested:
def detect_encoding(instream, encoding, detect_lines, skip_ascii=True):
if encoding is None:
encoding = instream.encoding
if encoding is None:
if skip_ascii:
try:
for line in instream:
yield line.decode("ascii")
except UnicodeDecodeError:
pass
else:
return
head = [line]
head.extend(islice(instream, detect_lines-1))
encoding = chardet.detect("".join(head))["encoding"]
instream = chain(head, instream)
for line in instream:
yield line.decode(encoding)
Or keep two lists, one with all, and one with only non-ascii lines, and read
lines until there are enough lines in the list of non-ascii strings to make
a good guess. Then take that list to determine the encoding.
You can even combine both approaches...
> - If the buffer was bigger than about some Megabytes, the returned
> encoding
> from libmagic was always None. The big files had very long lines ( more
> than 4k per line ). So with detect_lines=1000 this limit was exceeded.
>
> - The magic.buffer() ( the equivalent of chardet.detect() ) takes about 2
> seconds
> per megabyte buffer.
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