Retraining and storing data

[chardet]

Retraining and storing data

[dan-blanchard]

uchardet-enhanced actually has tools for retraining the C code, so we might not need to do this is we switch to just being a CFFI wrapper around that.

That said, uchardet-enhanced hasn't been touched in almost 3 years, so I'm a bit torn about relying on that. I'd also like to see the data files stored in a language-agnostic format, but that might come second to speed for most users.

[dan-blanchard]

Well, so much for that thought. I'm not convinced their updated tables are actually correct. If I swap cChardet in for chardet and run all of our unit tests, there are actually 53 test failures (vs our 1), so it looks like we're much slower but more accurate at this point.

[dan-blanchard]

I've created a new branch that makes chardet work like cChardet/uchardet-enhanced, but in pure Python. It's called feature/uchardet-enhanced-upstream. It performs worse than our current version, so it probably wasn't worth the effort. Oh well.

I have created 7 new language models for Central Europe countries. The romanian and hungarian language models can't distinguish between cp1250 and latin2 because all letters in romanian or hungarian alphabet have same place in both tables :-( . All new .py files with the modified sbcsgroupprober.py are in my repository and my fork.

[dan-blanchard]

The language models are intentionally language-specific (and not encoding-specific), so it's actually the character-to-order maps that index into the language model tables. Anyway, I don't know much about what subset of CP1250 is used for Hungarian and Romanian, but according to the table at the top of the Wikipedia article, it looks like at a minimum the Euro symbol and the quotation marks are in different places. Therefore, we should be able to differentiate between the two based on at least those characters.

If you have updated versions of the language models that work better in your fork, please create a pull request.

From wikipedia:
Windows-1250 is similar to ISO-8859-2 and has all the printable characters it has and more.
It means that ISO-8859-2 doesn't contains "special" quotation marks (U+201E,U+201C,U+201D) or Euro symbol, etc. Without these "more characters" in an analyzed text you can't distinguish between Latin2 and Cp1250. Simply said, the ISO-8859-2 is subset of the CP1250 and some chars are rearranged (big thanks M$). It means that every text in Romanian or Hungarian language (it isn't true for other Central Europen languages) which contains only iso-8859-2 characters can be treated as the Cp1250.
In my opinion, for such text is simple better to consider any iso-8859-2 as the cp1250, or create a test (in the sbcharsetprober.py) if the detected text contains any char from the "more characters", because the language models are based on bigrams (twochars sequences) testing which contains only the 64 most frequent letters (=no symbols).

I've created small script 'create_language_model.py' for building new python's language model files.
It needs 'CharsetsTabs.txt' file for correct running. Please read comments in the header.

[dan-blanchard]

#99 still uses Python language model files, but at least moves us in the right direction of allowing us to retrain at all.