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diff --git a/lib/python2.7/compiler/syntax.py b/lib/python2.7/compiler/syntax.py
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+"""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")