OPUS Parser

Fetch OPUS corpora for various language pairs. The library relies on xmltodict in order to use the streaming mode for large TMX files.

Quickstart

Clone the repository and build a Docker image after installing Docker for your platform.

cd opus_tmx_parser
docker build -t opus_tmx_parser .

Simply run the built Docker image with the options for source -s (always English en) and target -t language:

docker run -v ~/data_host:/data/ opus_tmx_parser -t lv

You can set the data directory for the TMX files with the -v/--volume option.

Setup

Install required packages

rake setup:install

Run after install

The standard corpus (controlled with -c option) is ParaCrawl. To get a list of available corpora check: http://opus.nlpl.eu/opusapi/?corpora=True

./opus_tmx_parser.py -s en -t lt

If you want to get data for all corpora use the -a this will ignore the -c parameter.

./opus_tmx_parser.py -t lt -a

Development

linter

Test code quality

rake dev:lint

clean environment

Remove old cache files

rake dev:clean

Options and Explanation

• The script has 1 mandatory argument for the target language -t. OPUS releases several corpora by default ParaCrawl is used but with the -c option other corpora can be picked or all corpora -a for one language pair.
• The script uses the OPUS API to verify that the corpus exists and that the corpus offers the specified languages. If not the script will log an error.
• If the (sometimes very large) TMX data is not already downloaded it will be fetched with python-requests. The progress of the download is logged with tqdm.
• Since the data can be very large it is best not to read to whole file into memory but instead use an xml library with streaming functionality like xmltodict that processes the file iteratively.
• The output can also be written iteratively to keep the memory footprint small by appending to the output files line by line. Therefore you see the script occassionally logging how many lines have been written. To change the number of written lines at a time use -l.
• If there should be a maximum limit of written lines for a corpus use -m. If it is used together with -a then the sum of lines from each corpus will be approximately the amount in -m.
• Since data is appended to the output files in order to process the TMX files iteratively, it is necessary to delete former files. Otherwise if the script terminates there are duplicate lines when re-running with the same parameters. The option -k controls if the files should be appended and not deleted instead.

Notes

A sample output of running the script with docker docker run -v ~/data_host:/data/ opus_tmx_parser -s en -t lv.

2020-05-21 18:27:40,577 INFO: (opus_tmx_parser.py:260) No TMX file /data/en-lv.tmx.gz for input languages en-lv found.
2020-05-21 18:27:41,190 INFO: (opus_tmx_parser.py:108) Corpus information [{'alignment_pairs': 1019003, 'corpus': 'ParaCrawl', 'documents': 21, 'id': 264034, 'latest': 'True', 'preprocessing': 'tmx', 'size': 292192, 'source': 'en', 'source_tokens': 26868814, 'target': 'lv', 'target_tokens': 24032548, 'url': 'https://object.pouta.csc.fi/OPUS-ParaCrawl/v5/tmx/en-lv.tmx.gz', 'version': 'v5'}]
2020-05-21 18:27:41,190 INFO: (opus_tmx_parser.py:117) Fetching TMX file from https://object.pouta.csc.fi/OPUS-ParaCrawl/v5/tmx/en-lv.tmx.gz
100%|██████████| 299M/299M [00:33<00:00, 8.87MiB/s]
2020-05-21 18:28:15,314 INFO: (opus_tmx_parser.py:299) Deleting pre-exisiting files /data/ParaCrawl_en.txt and /data/ParaCrawl_lv.txt
2020-05-21 18:28:15,325 INFO: (opus_tmx_parser.py:309) Processing /data/en-lv.tmx.gz writing every 300,000 lines to /data/ParaCrawl_lv.txt and /data/ParaCrawl_en.txt
2020-05-21 18:29:16,538 INFO: (opus_tmx_parser.py:230) Writing 300,000 lines of language pairs.
2020-05-21 18:30:27,960 INFO: (opus_tmx_parser.py:230) Writing 300,000 lines of language pairs.
2020-05-21 18:31:33,603 INFO: (opus_tmx_parser.py:230) Writing 300,000 lines of language pairs.
2020-05-21 18:32:12,146 INFO: (opus_tmx_parser.py:230) Writing 119,003 lines of language pairs.

Remarks:

• There is an issue in xmltodict that talks about making the streaming mode more pythonic with a generator. It would have been a nicer approach than using a callback function because it would avoid the global variable _LANGUAGE_PAIRS that was used.
• For a combination like Afrikaans and Greek in OpenSubtitles the number of alignment_pairs is 31 774 however looking at the file directly there are 116 017 lines with tu elements. Therefore the number of pairs is 116 017 / 2 / 2 = 29 004 (dividing by number of tu start and end lines, and tuv element lines). That is also the output when calling the script ./opus_tmx_parser.py -s af -t el -c OpenSubtitles. Thus, I didn't include this number to include a progress bar since it's not reliable. Because the solution is iterative there is no certainty how many lines there are and when the script approximately finishes.
• There is an available library for fetching OPUS data but it's designed as command line tools. This library showcases how to use the API.
• I would like to further explorer memory consumption and execution speed between xmltodict and lxml.