# Natural Language Toolkit: Simple Tokenizers
#
# Copyright (C) 2001-2008 NLTK Project
# Author: Edward Loper <edloper@gradient.cis.upenn.edu>
#         Steven Bird <sb@csse.unimelb.edu.au>
#         Trevor Cohn <tacohn@csse.unimelb.edu.au>
# URL: <http://nltk.sourceforge.net>
# For license information, see LICENSE.TXT

"""
Tokenizers that divide strings into substrings using the string
C{split()} method.

These tokenizers follow the standard L{TokenizerI} interface, and so
can be used with any code that expects a tokenizer.  For example,
these tokenizers can be used to specify the tokenization conventions
when building a L{CorpusReader<nltk.corpus.reader.api.CorpusReader>}.
But if you are tokenizing a string yourself, consider using string
C{split()} method directly instead.
"""

from api import *

class WhitespaceTokenizer(TokenizerI):
    r"""
    A tokenizer that divides a string into substrings by treating any
    sequence of whitespace characters as a separator.  Whitespace
    characters are space (C{' '}), tab (C{'\t'}), and newline
    (C{'\n'}).  If you are performing the tokenization yourself
    (rather than building a tokenizer to pass to some other piece of
    code), consider using the string C{split()} method instead:

        >>> words = s.split()
    """
    def tokenize(self, s):
        return s.split()

class SpaceTokenizer(TokenizerI):
    r"""
    A tokenizer that divides a string into substrings by treating any
    single space character as a separator.  If you are performing the
    tokenization yourself (rather than building a tokenizer to pass to
    some other piece of code), consider using the string C{split()}
    method instead:

        >>> words = s.split(' ')
    """
    def tokenize(self, s):
        return s.split(' ')

class TabTokenizer(TokenizerI):
    r"""
    A tokenizer that divides a string into substrings by treating any
    single tab character as a separator.  If you are performing the
    tokenization yourself (rather than building a tokenizer to pass to
    some other piece of code), consider using the string C{split()}
    method instead:

        >>> words = s.split('\t')
    """
    def tokenize(self, s):
        return s.split('\t')

class LineTokenizer(TokenizerI):
    r"""
    A tokenizer that divides a string into substrings by treating any
    single newline character as a separator.  Handling of blank lines
    may be controlled using a constructor parameter.
    """
    def __init__(self, blanklines='discard'):
        """
        @param blanklines: Indicates how blank lines should be
        handled.  Valid values are:
        
          - C{'discard'}: strip blank lines out of the token list
            before returning it.  A line is considered blank if
            it contains only whitespace characters.
          - C{'keep'}: leave all blank lines in the token list.
          - C{'discard-eof'}: if the string ends with a newline,
            then do not generate a corresponding token C{''} after
            that newline.
        """
        valid_blanklines = ('discard', 'keep', 'discard-eof')
        if blanklines not in valid_blanklines:
            raise ValueError('Blank lines must be one of: %s' %
                             ' '.join(valid_blanklines))
            
        self._blanklines = blanklines
    
    def tokenize(self, s):
        lines = s.split('\n')
        # If requested, strip off blank lines.
        if self._blanklines == 'discard':
            lines = [l for l in lines if l.rstrip()]
        elif self._blanklines == 'discard-eof':
            if lines and not lines[-1].strip(): lines.pop()
        return lines

######################################################################
#{ Tokenization Functions
######################################################################

def line_tokenize(text, blanklines='discard'):
    return LineTokenizer(blanklines).tokenize(text)
