A tokenizer for Icelandic text
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README.rst

Tokenizer: A tokenizer for Icelandic text

Overview

Tokenization is a necessary first step in many natural language processing tasks, such as word counting, parsing, spell checking, corpus generation, and statistical analysis of text.

Tokenizer is a compact pure-Python (2 and 3) module for tokenizing Icelandic text. It converts Python text strings to streams of token objects, where each token object is a separate word, punctuation sign, number/amount, date, e-mail, URL/URI, etc. It also segments the token stream into sentences, considering corner cases such as abbreviations and dates in the middle of sentences.

The package contains a dictionary of common Icelandic abbreviations, in the file src/tokenizer/Abbrev.conf.

Tokenizer is derived from a corresponding module in the Greynir project (GitHub repository here), by the same authors. Note that Tokenizer is licensed under the MIT license while Greynir is licensed under GPLv3.

You might also find the Reynir natural language parser for Icelandic interesting. The Reynir parser uses Tokenizer on its input.

To install:

$ pip install tokenizer

To use (for Python 3, you can omit the u"" string prefix):

from tokenizer import tokenize, TOK

text = (u"Málinu var vísað til stjórnskipunar- og eftirlitsnefndar "
        u"skv. 3. gr. XVII. kafla laga nr. 10/2007 þann 3. janúar 2010.")

for token in tokenize(text):

        print(u"{0}: '{1}' {2}".format(
                TOK.descr[token.kind],
                token.txt or "-",
                token.val or ""))

Output:

BEGIN SENT: '-' (0, None)
WORD: 'Málinu'
WORD: 'var'
WORD: 'vísað'
WORD: 'til'
WORD: 'stjórnskipunar- og eftirlitsnefndar'
WORD: 'skv.' [('samkvæmt', 0, 'fs', 'skst', 'skv.', '-')]
ORDINAL: '3.' 3
WORD: 'gr.' [('grein', 0, 'kvk', 'skst', 'gr.', '-')]
ORDINAL: 'XVII.' 17
WORD: 'kafla'
WORD: 'laga'
WORD: 'nr.' [('númer', 0, 'hk', 'skst', 'nr.', '-')]
NUMBER: '10' (10, None, None)
PUNCTUATION: '/' 4
YEAR: '2007' 2007
WORD: 'þann'
DATEABS: '3. janúar 2010' (2010, 1, 3)
PUNCTUATION: '.' 3
END SENT: '-'

Note the following:

  • Sentences are delimited by TOK.S_BEGIN and TOK.S_END tokens.
  • Composite words, such as stjórnskipunar- og eftirlitsnefndar, are coalesced into one token.
  • Well-known abbreviations are recognized and their full expansion is available in the token.val field.
  • Ordinal numbers (3., XVII.) are recognized and their value (3, 17) is available in the token.val field.
  • Dates, years and times, both absolute and relative, are recognized and the respective year, month, day, hour, minute and second values are included as a tuple in token.val.
  • Numbers, both integer and real, are recognized and their value is available in the token.val field.
  • Further details of how Tokenizer processes text can be inferred from the test module in the project's GitHub repository.

The tokenize() function

To tokenize a text string, call tokenizer.tokenize(text). This function returns a Python generator of token objects. Each token object is a simple namedtuple with three fields: (kind, txt, val) (see below).

The tokenizer.tokenize() function is typically called in a for loop:

for token in tokenizer.tokenize(mystring):
        kind, txt, val = token
        if kind == tokenizer.TOK.WORD:
                # Do something with word tokens
                pass
        else:
                # Do something else
                pass

Alternatively, create a token list from the returned generator:

token_list = list(tokenizer.tokenize(mystring))

In Python 2.7, you can pass either unicode strings or str byte strings to tokenizer.tokenize(). In the latter case, the byte string is assumed to be encoded in UTF-8.

The token object

Each token is represented by a namedtuple with three fields: (kind, txt, val).

The kind field

The kind field contains one of the following integer constants, defined within the TOK class:

Constant Value Explanation Examples
PUNCTUATION 1 Punctuation .
TIME 2 Time (h, m, s) 11:35:40
DATE * 3 Date (y, m, d) [Unused, see DATEABS and DATEREL]
YEAR 4 Year
árið 874 e.Kr.
1965
44 f.Kr.
NUMBER 5 Number
100
1.965
1.965,34
1,965.34
WORD 6 Word
kattaeftirlit
hunda- og kattaeftirlit
TELNO 7 Telephone number
123444
123-4444
PERCENT 8 Percentage 78%
URL 9 URL
https://greynir.is
www.greynir.is
ORDINAL 10 Ordinal number
30.
XVIII.
TIMESTAMP * 11 Timestamp [Unused, see TIMESTAMPABS and TIMESTAMPREL]
CURRENCY * 12 Currency name [Unused]
AMOUNT 13 Amount
€2.345,67
750 þús.kr.
2,7 mrð. USD
PERSON * 14 Person name [Unused]
EMAIL 15 E-mail fake@news.is
ENTITY * 16 Named entity [Unused]
UNKNOWN 17 Unknown token  
DATEABS 18 Absolute date
30. desember 1965
30/12/1965
1965-12-30
DATEREL 19 Relative date
  1. mars
TIMESTAMPABS 20 Absolute timestamp
30. desember 1965 11:34
1965-12-30 kl. 13:00
TIMESTAMPREL 21 Relative timestamp
  1. desember kl. 13:00
MEASUREMENT 22 Value with a measurement unit
690 MW
1.010 hPa
220 m²
NUMWLETTER 23 Number followed by a single letter
14a
7B
S_BEGIN 11001 Start of sentence  
S_END 11002 End of sentence  

(*) The token types marked with an asterisk are reserved for the Reynir package and not currently returned by the tokenizer.

To obtain a descriptive text for a token kind, use TOK.descr[token.kind] (see example above).

The txt field

The txt field contains the original source text for the token. However, in a few cases, the tokenizer auto-corrects the original source text:

  • It converts single and double quotes to the correct Icelandic ones (i.e. „these“ or ‚these‘).
  • It converts kludgy ordinals (3ja) to proper ones (þriðja), and English-style thousand and decimal separators to Icelandic ones (10,345.67 becomes 10.345,67).
  • Tokenizer automatically merges Unicode COMBINING ACUTE ACCENT (code point 769) and COMBINING DIAERESIS (code point 776) with vowels to form single code points for the Icelandic letters á, é, í, ó, ú, ý and ö, in both lower and upper case.

In the case of abbreviations that end a sentence, the final period '.' is a separate token, and it is consequently omitted from the abbreviation token's txt field. A sentence ending in o.s.frv. will thus end with two tokens, the next-to-last one being the tuple (TOK.WORD, "o.s.frv", "og svo framvegis") - note the omitted period in the txt field - and the last one being (TOK.PUNCTUATION, ".", 3) (the 3 is explained below).

The val field

The val field contains auxiliary information, corresponding to the token kind, as follows:

  • For TOK.PUNCTUATION, the val field specifies the whitespace normally found around the symbol in question:

    TP_LEFT = 1   # Whitespace to the left
    TP_CENTER = 2 # Whitespace to the left and right
    TP_RIGHT = 3  # Whitespace to the right
    TP_NONE = 4   # No whitespace
    
  • For TOK.TIME, the val field contains an (hour, minute, second) tuple.

  • For TOK.DATEABS, the val field contains a (year, month, day) tuple (all 1-based).

  • For TOK.DATEREL, the val field contains a (year, month, day) tuple (all 1-based), except that a least one of the tuple fields is missing and set to 0. Example: þriðja júní becomes TOK.DATEREL with the fields (0, 6, 3) as the year is missing.

  • For TOK.YEAR, the val field contains the year as an integer. A negative number indicates that the year is BCE (fyrir Krist), specified with the suffix f.Kr. (e.g. árið 33 f.Kr.).

  • For TOK.NUMBER, the val field contains a tuple (number, None, None). (The two empty fields are included for compatibility with Greynir.)

  • For TOK.WORD, the val field contains the full expansion of an abbreviation, as a list containing a single tuple, or None if the word is not abbreviated.

  • For TOK.PERCENT, the val field contains a tuple of (percentage, None, None).

  • For TOK.ORDINAL, the val field contains the ordinal value as an integer. The original ordinal may be a decimal number or a Roman numeral.

  • For TOK.TIMESTAMP, the val field contains a (year, month, day, hour, minute, second) tuple.

  • For TOK.AMOUNT, the val field contains an (amount, currency, None, None) tuple. The amount is a float, and the currency is an ISO currency code, e.g. USD for dollars ($ sign), EUR for euros (€ sign) or ISK for Icelandic króna (kr. abbreviation). (The two empty fields are included for compatibility with Greynir.)

  • For TOK.MEASUREMENT, the val field contains a (unit, value) tuple, where unit is a base SI unit (such as g, m, , s, W, Hz, K for temperature in Kelvin).

The correct_spaces() function

Tokenizer also contains the utility function tokenizer.correct_spaces(text). This function returns a string after splitting it up and re-joining it with correct whitespace around punctuation tokens. Example:

>>> tokenizer.correct_spaces("Frétt \n  dagsins:Jón\t ,Friðgeir og Páll ! 100  /  2  =   50")
'Frétt dagsins: Jón, Friðgeir og Páll! 100/2 = 50'

The Abbrev.conf file

Abbreviations recognized by Tokenizer are defined in the Abbrev.conf file, found in the src/tokenizer/ directory. This is a text file with abbreviations, their definitions and explanatory comments. The file is loaded into memory during the first call to tokenizer.tokenize() within a process.

Development installation

To install Tokenizer in development mode, where you can easily modify the source files (assuming you have git available):

$ git clone https://github.com/vthorsteinsson/Tokenizer
$ cd Tokenizer
$ # [ Activate your virtualenv here, if you have one ]
$ python setup.py develop

To run the built-in tests, install pytest, cd to your Tokenizer subdirectory (and optionally activate your virtualenv), then run:

$ python -m pytest

Changelog

  • Version 1.0.7: Added NUMWLETTER token type
  • Version 1.0.6: Automatic merging of Unicode COMBINING ACUTE ACCENT and COMBINING DIAERESIS code points with vowels
  • Version 1.0.5: Date/time and amount tokens coalesced to a further extent
  • Version 1.0.4: Added TOK.DATEABS, TOK.TIMESTAMPABS, TOK.MEASUREMENT