tokenizer 1.0.4

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))

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
PERSON *	14	Person name	[Unused]
EMAIL	15	E-mail	[e-mail]
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	mars
TIMESTAMPABS	20	Absolute timestamp	30. desember 1965 11:34 1965-12-30 kl. 13:00
TIMESTAMPREL	21	Relative timestamp	desember kl. 13:00
MEASUREMENT	22	Value with a measurement unit	690 MW 1.010 hPa 220 m²
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. For instance, it converts single and double quotes to the correct Icelandic ones (i.e. „these“ or ‚these‘). It also 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).

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, i.e. USD for dollars ($ sign) or EUR for euros (€ sign). (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, m², 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 1.0.4: Added TOK.DATEABS, TOK.TIMESTAMPABS, TOK.MEASUREMENT