Use <<= instead of deprecated << in SPARQL parser

[bogdan-kulynych]

Allows to use newer pyparsing (>=2.0.1) without getting deprecation warnings:

pyparsing.py:3546: DeprecationWarning: Operator '<<' is deprecated, use '<<=' instead
  ret << Group( Suppress(opener) + ZeroOrMore( ignoreExpr | ret | content ) + Suppress(closer) )

Addresses inveniosoftware/invenio#2077

[gromgull]

Great! I saw they added this at some point, but I never got around to updating the sparql parser.

Any idea why the tests fail on 2.X though?

[bogdan-kulynych]

It looks like pyparsing 1.5.7 (requirements.py2.txt), always returns None as a result of __lshift__:

def __lshift__( self, other ):
    if isinstance( other, basestring ):
        other = ParserElement.literalStringClass(other)
    self.expr = other
    self.mayReturnEmpty = other.mayReturnEmpty
    self.strRepr = None
    self.mayIndexError = self.expr.mayIndexError
    self.mayReturnEmpty = self.expr.mayReturnEmpty
    self.setWhitespaceChars( self.expr.whiteChars )
    self.skipWhitespace = self.expr.skipWhitespace
    self.saveAsList = self.expr.saveAsList
    self.ignoreExprs.extend(self.expr.ignoreExprs)
    return None
__ilshift__ = __lshift__

whereas pyparsing 2.0.2 (requirements.py3.txt) returns self. Returning self fixes the test failures. Should I maybe monkeypatch the __lshift__ method? :-/

[gromgull]

we'll upgrade to pyparsing 2 for all version for v5 and merge it then.