def __init__(self, constants=None, version=VERSION_FLAG_STYLE):
<EOL>if constants is None:<EOL><INDENT>self.ptc = Constants()<EOL><DEDENT>else:<EOL><INDENT>self.ptc = constants<EOL><DEDENT>self.version = version<EOL>if version == VERSION_FLAG_STYLE:<EOL><INDENT>warnings.warn(<EOL>'<STR_LIT>'<EOL>'<STR_LIT>'<EOL>'<STR_LIT>',<EOL>pdt20DeprecationWarning)<EOL><DEDENT>self._ctxStack = pdtContextStack()<EOL>
Default constructor for the L{Calendar} class.

@type  constants: object
@param constants: Instance of the class L{Constants}
@type  version:   integer
@param version:   Default style version of current Calendar instance.
                  Valid value can be 1 (L{VERSION_FLAG_STYLE}) or
                  2 (L{VERSION_CONTEXT_STYLE}). See L{parse()}.

@rtype:  object
@return: L{Calendar} instance