[Pyparsing] setDefaultWhitespaceChars

[<mmm...@gm...>]

I am trying to make "\t" significant by passing a string that doesn't  
include "\t" to setDefaultWhitespaceChars.
However, it still seems to recognize '\t' as a white space.

>>> ParserElement.setDefaultWhitespaceChars("\n\r ")

>>> words = Word(alphas)

>>> sentence = OneOrMore(words) + '.'

>>> print sentence.parseString("\tHello World.")

['Hello', 'World', '.']


How should I accomplish this?