"""Check for errs in the AST.

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

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assignments with invalid targets, are caught in the code generation

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phase.

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The compiler package catches some errors in the transformer module.

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

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errors.

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"""

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from compiler import ast, walk

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def check(tree, multi=None):

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v = SyntaxErrorChecker(multi)

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walk(tree, v)

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return v.errors

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class SyntaxErrorChecker:

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

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def __init__(self, multi=None):

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"""Create new visitor object.

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If optional argument multi is not None, then print messages

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for each error rather than raising a SyntaxError for the

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first.

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"""

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self.multi = multi

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self.errors = 0

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def error(self, node, msg):

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self.errors = self.errors + 1

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if self.multi is not None:

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

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else:

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

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def visitAssign(self, node):

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# the transformer module handles many of these

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pass

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## for target in node.nodes:

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

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## if target.lineno is None:

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## target.lineno = node.lineno

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

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