__init__ (
        self,
        expression,
        invert=0,
        )

(expression, invert = 0)

A non-consuming assertion using the given expression. The default is a positive lookahead, which matches if the expression matches at the current position, but does not affect the character position.

If invert is false, this is a negative lookahead assertion, and matches if the expression does not match. Again, the character position is not affected.

__str__ ( self )

the corresponding pattern string

copy ( self )

do a deep copy on this Expression tree