This python string literals documentation<http://docs.python.org/2/reference/lexical_analysis.html#string-literals>couldn't explain: single quote presence inside double quoted string and viceversa. I think both double quoted string and single quoted string need to be defined differently for representing the 'stringliteral' lexical definition. shortstringchar ::= <any source character except "\" or newline or the quote> here in this definition 'the quote' isn't specific whether single (') or double ("). I asked this question here, http://stackoverflow.com/questions/16435233/this-python-string-literals-docu..., . I was advised to ask here -- Alok Nayak Gwalior, India -- Alok Nayak Gwalior, India