checker.py: Check for invalid print syntax

New warning added in messages.py to check for invalid
print syntax

Closes #242

Author: ankitxjoshi

pyflakes/checker.py

@@ -768,6 +768,13 @@ def handleNodeLoad(self, node):
                     # iteration
                     continue
 
+            if (name == 'print' and
+                    isinstance(scope.get(name, None), Builtin)):
+                parent = self.getParent(node)
+                if (isinstance(parent, ast.BinOp) and
+                        isinstance(parent.op, ast.RShift)):
+                    self.report(messages.InvalidPrintSyntax, node)
+
             try:
                 scope[name].used = (self.scope, node)
             except KeyError:

pyflakes/messages.py

@@ -250,3 +250,7 @@ def __init__(self, filename, loc, annotation):
 
 class RaiseNotImplemented(Message):
     message = "'raise NotImplemented' should be 'raise NotImplementedError'"
+
+
+class InvalidPrintSyntax(Message):
+    message = 'use of >> is invalid with print function'

pyflakes/test/test_other.py

@@ -2034,3 +2034,53 @@ def test_raise_notimplemented(self):
         self.flakes('''
         raise NotImplemented
         ''', m.RaiseNotImplemented)
+
+
+class TestIncompatiblePrintOperator(TestCase):
+    """
+    Tests for warning about invalid use of print function.
+    """
+
+    def test_valid_print(self):
+        self.flakes('''
+        print("Hello")
+        ''')
+
+    def test_invalid_print_when_imported_from_future(self):
+        exc = self.flakes('''
+        from __future__ import print_function
+        import sys
+        print >>sys.stderr, "Hello"
+        ''', m.InvalidPrintSyntax).messages[0]
+
+        self.assertEqual(exc.lineno, 4)
+        self.assertEqual(exc.col, 0)
+
+    def test_print_function_assignment(self):
+        """
+        A valid assignment, tested for catching false positives.
+        """
+        self.flakes('''
+        from __future__ import print_function
+        log = print
+        log("Hello")
+        ''')
+
+    def test_print_in_lambda(self):
+        self.flakes('''
+        from __future__ import print_function
+        a = lambda: print
+        ''')
+
+    def test_print_returned_in_function(self):
+        self.flakes('''
+        from __future__ import print_function
+        def a():
+            return print
+        ''')
+
+    def test_print_as_condition_test(self):
+        self.flakes('''
+        from __future__ import print_function
+        if print: pass
+        ''')