"""Check for errs in the AST.

The Python parser does not catch all syntax errors.  Others, like

assignments with invalid targets, are caught in the code generation

phase.

The compiler package catches some errors in the transformer module.

But it seems clearer to write checkers that use the AST to detect

errors.

"""

from compiler import ast, walk

def check(tree, multi=None):

    v = SyntaxErrorChecker(multi)

    walk(tree, v)

    return v.errors

class SyntaxErrorChecker:

    """A visitor to find syntax errors in the AST."""

    def __init__(self, multi=None):

        """Create new visitor object.

        If optional argument multi is not None, then print messages

        for each error rather than raising a SyntaxError for the

        first.

        """

        self.multi = multi

        self.errors = 0

    def error(self, node, msg):

        self.errors = self.errors + 1

        if self.multi is not None:

            print "%s:%s: %s" % (node.filename, node.lineno, msg)

        else:

            raise SyntaxError, "%s (%s:%s)" % (msg, node.filename, node.lineno)

    def visitAssign(self, node):

        # the transformer module handles many of these

        pass

##        for target in node.nodes:

##            if isinstance(target, ast.AssList):

##                if target.lineno is None:

##                    target.lineno = node.lineno

##                self.error(target, "can't assign to list comprehension")