Fix print() function on Python 2 (#754)

Fixes #752

black.py

@@ -726,13 +726,13 @@ def get_grammars(target_versions: Set[TargetVersion]) -> List[Grammar]:
     if not target_versions:
         return GRAMMARS
     elif all(not version.is_python2() for version in target_versions):
-        # Python 2-compatible code, so don't try Python 3 grammar.
+        # Python 3-compatible code, so don't try Python 2 grammar
         return [
             pygram.python_grammar_no_print_statement_no_exec_statement,
             pygram.python_grammar_no_print_statement,
         ]
     else:
-        return [pygram.python_grammar]
+        return [pygram.python_grammar_no_print_statement, pygram.python_grammar]
 
 
 def lib2to3_parse(src_txt: str, target_versions: Iterable[TargetVersion] = ()) -> Node:

tests/data/python2_print_function.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python2
+from __future__ import print_function
+
+print('hello')
+print(u'hello')
+print(a, file=sys.stderr)
+
+# output
+
+
+#!/usr/bin/env python2
+from __future__ import print_function
+
+print("hello")
+print(u"hello")
+print(a, file=sys.stderr)

tests/test_black.py

@@ -461,6 +461,14 @@ def test_python2(self) -> None:
         # black.assert_equivalent(source, actual)
         black.assert_stable(source, actual, black.FileMode())
 
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_python2_print_function(self) -> None:
+        source, expected = read_data("python2_print_function")
+        mode = black.FileMode(target_versions={black.TargetVersion.PY27})
+        actual = fs(source, mode=mode)
+        self.assertFormatEqual(expected, actual)
+        black.assert_stable(source, actual, mode)
+
     @patch("black.dump_to_file", dump_to_stderr)
     def test_python2_unicode_literals(self) -> None:
         source, expected = read_data("python2_unicode_literals")