WIP: futurize --conservative option

Add unit tests (not yet working) for a --conservative option to futurize that
converts even difficult Py2 code to run on both Py2 and Py3.

Author: edschofield

future/tests/base.py

@@ -138,7 +138,7 @@ def setUp(self):
         self.env = {'PYTHONPATH': os.getcwd()}
 
     def convert(self, code, stages=(1, 2), all_imports=False, from3=False,
-                reformat=True, run=True):
+                reformat=True, run=True, conservative=False):
         """
         Converts the code block using ``futurize`` and returns the
         resulting code.
@@ -160,7 +160,7 @@ def convert(self, code, stages=(1, 2), all_imports=False, from3=False,
             code = reformat_code(code)
         self._write_test_script(code)
         self._futurize_test_script(stages=stages, all_imports=all_imports,
-                                   from3=from3)
+                                   from3=from3, conservative=conservative)
         output = self._read_test_script()
         if run:
             for interpreter in self.interpreters:
@@ -219,7 +219,8 @@ def strip_future_imports(self, code):
         return '\n'.join(output)
 
     def convert_check(self, before, expected, stages=(1, 2), all_imports=False,
-                      ignore_imports=True, from3=False, run=True):
+                      ignore_imports=True, from3=False, run=True,
+                      conservative=False):
         """
         Convenience method that calls convert() and compare().
 
@@ -239,7 +240,7 @@ def convert_check(self, before, expected, stages=(1, 2), all_imports=False,
         for the purpose of the comparison.
         """
         output = self.convert(before, stages=stages, all_imports=all_imports,
-                              from3=from3, run=run)
+                              from3=from3, run=run, conservative=conservative)
         if all_imports:
             headers = self.headers2 if 2 in stages else self.headers1
         else:
@@ -272,7 +273,8 @@ def _read_test_script(self, filename='mytestscript.py'):
         return newsource
 
     def _futurize_test_script(self, filename='mytestscript.py', stages=(1, 2),
-                              all_imports=False, from3=False):
+                              all_imports=False, from3=False,
+                              conservative=False):
         params = []
         stages = list(stages)
         if all_imports:
@@ -287,6 +289,8 @@ def _futurize_test_script(self, filename='mytestscript.py', stages=(1, 2),
                 params.append('--stage2')
             else:
                 assert stages == [1, 2]
+            if conservative:
+                params.append('--conservative')
             # No extra params needed
 
         output = subprocess.check_output([sys.executable, script] + params +

future/tests/test_futurize.py

@@ -1032,6 +1032,83 @@ def test_issue_12(self):
         """
         self.unchanged(code)
 
+    def test_range_necessary_list_calls(self):
+        before = """
+        l = range(10)
+        assert isinstance(l, list)
+        for i in range(3):
+            print i
+        for i in xrange(3):
+            print i
+        """
+        after = """
+        from __future__ import print_function
+        from future.builtins import range
+        l = list(range(10))
+        assert isinstance(l, list)
+        for i in range(3):
+            print(i)
+        for i in range(3):
+            print(i)
+        """
+        self.convert_check(before, after)
+
+
+class TestConservativeFuturize(CodeHandler):
+    @unittest.expectedFailure
+    def test_basestring(self):
+        """
+        In conservative mode, futurize would not modify "basestring"
+        but merely import it, and the following code would still run on
+        both Py2 and Py3.
+        """
+        before = """
+        assert isinstance('hello', basestring)
+        assert isinstance(u'hello', basestring)
+        assert isinstance(b'hello', basestring)
+        """
+        after = """
+        from past.builtins import basestring
+        assert isinstance('hello', basestring)
+        assert isinstance(u'hello', basestring)
+        assert isinstance(b'hello', basestring)
+        """
+        self.convert_check(before, after, conservative=True)
+
+    @unittest.expectedFailure
+    def test_open(self):
+        """
+        In conservative mode, futurize would not import io.open because
+        this changes the default return type from bytes to text.
+        """
+        before = """
+        filename = 'temp_file_open.test'
+        contents = 'Temporary file contents. Delete me.'
+        with open(filename, 'w') as f:
+            f.write(contents)
+
+        with open(filename, 'r') as f:
+            data = f.read()
+        assert isinstance(data, str)
+        assert data == contents
+        """
+        after = """
+        from past.builtins import open, str as oldbytes, unicode
+        filename = oldbytes(b'temp_file_open.test')
+        contents = oldbytes(b'Temporary file contents. Delete me.')
+        with open(filename, oldbytes(b'w')) as f:
+            f.write(contents)
+
+        with open(filename, oldbytes(b'r')) as f:
+            data = f.read()
+        assert isinstance(data, oldbytes)
+        assert data == contents
+        assert isinstance(oldbytes(b'hello'), basestring)
+        assert isinstance(unicode(u'hello'), basestring)
+        assert isinstance(oldbytes(b'hello'), basestring)
+        """
+        self.convert_check(before, after, conservative=True)
+
     def test_safe_division(self):
         """
         Tests whether Py2 scripts using old-style division still work
@@ -1087,27 +1164,6 @@ def __truediv__(self, other):
         """
         self.convert_check(before, after)
 
-    def test_range_necessary_list_calls(self):
-        before = """
-        l = range(10)
-        assert isinstance(l, list)
-        for i in range(3):
-            print i
-        for i in xrange(3):
-            print i
-        """
-        after = """
-        from __future__ import print_function
-        from future.builtins import range
-        l = list(range(10))
-        assert isinstance(l, list)
-        for i in range(3):
-            print(i)
-        for i in range(3):
-            print(i)
-        """
-        self.convert_check(before, after)
-
 
 if __name__ == '__main__':
     unittest.main()