1"""Check for errs in the AST.
2
3The Python parser does not catch all syntax errors.  Others, like
4assignments with invalid targets, are caught in the code generation
5phase.
6
7The compiler package catches some errors in the transformer module.
8But it seems clearer to write checkers that use the AST to detect
9errors.
10"""
11
12from compiler import ast, walk
13
14def check(tree, multi=None):
15    v = SyntaxErrorChecker(multi)
16    walk(tree, v)
17    return v.errors
18
19class SyntaxErrorChecker:
20    """A visitor to find syntax errors in the AST."""
21
22    def __init__(self, multi=None):
23        """Create new visitor object.
24
25        If optional argument multi is not None, then print messages
26        for each error rather than raising a SyntaxError for the
27        first.
28        """
29        self.multi = multi
30        self.errors = 0
31
32    def error(self, node, msg):
33        self.errors = self.errors + 1
34        if self.multi is not None:
35            print "%s:%s: %s" % (node.filename, node.lineno, msg)
36        else:
37            raise SyntaxError, "%s (%s:%s)" % (msg, node.filename, node.lineno)
38
39    def visitAssign(self, node):
40        # the transformer module handles many of these
41        pass
42##        for target in node.nodes:
43##            if isinstance(target, ast.AssList):
44##                if target.lineno is None:
45##                    target.lineno = node.lineno
46##                self.error(target, "can't assign to list comprehension")
47