Merge pull request #110 from python-modernize/fix_classic_division

Add a classic_division fixer.

Author: daira

CHANGELOG.rst

@@ -2,7 +2,11 @@ Unreleased
 ==========
 
 Changes since 0.4:
+
+* Added the opt-in classic_division fixer.
 * Updated the ``dict_six`` fixer to support ``six.viewitems()`` and friends.
+* Documentation corrections.
+
 
 Version 0.4
 ===========

docs/fixers.rst

@@ -281,6 +281,27 @@ to specify the ``-f default`` or ``--fix=default`` option, e.g.::
 
     python-modernize -f default -f libmodernize.fixes.fix_open
 
+.. 2to3fixer:: classic_division
+
+   When a use of the division operator -- ``/`` -- is found, add
+   ``from __future__ import division`` and change the operator to ``//``.
+   If ``from __future__ import division`` is already present, this fixer is
+   skipped.
+
+   This is intended for use in programs where ``/`` is conventionally only used
+   for integer division, or where it is intended to do a manual pass after running
+   python-modernize to look for cases that should not have been changed to ``//``.
+   The results of division on non-integers may differ after running this fixer:
+   for example, ``3.5 / 2 == 1.75``, but ``3.5 // 2 == 1.0``.
+
+   Some objects may override the ``__div__`` method for a use other than division,
+   and thus would break when changed to use a ``__floordiv__`` method instead.
+
+   This fixer is opt-in because it may change the meaning of code as described
+   above.
+
+   .. versionadded:: 0.5
+
 .. 2to3fixer:: open
 
    When a call to :func:`open <python2:open>` is discovered, add ``from io import open`` at the top

libmodernize/fixes/__init__.py

@@ -45,5 +45,6 @@
 
 # Fixes that are opt-in only.
 opt_in_fix_names = set([
+    'libmodernize.fixes.fix_classic_division',
     'libmodernize.fixes.fix_open',
 ])

libmodernize/fixes/fix_classic_division.py

@@ -0,0 +1,24 @@
+from __future__ import absolute_import
+
+from lib2to3 import fixer_base
+from lib2to3 import pytree
+from lib2to3.pgen2 import token
+
+import libmodernize
+
+
+class FixClassicDivision(fixer_base.BaseFix):
+    _accept_type = token.SLASH
+
+    def start_tree(self, tree, name):
+        super(FixClassicDivision, self).start_tree(tree, name)
+        self.skip = "division" in tree.future_features
+
+    def match(self, node):
+        return node.value == "/"
+
+    def transform(self, node, results):
+        if self.skip:
+            return
+        libmodernize.add_future(node, u'division')
+        return pytree.Leaf(token.SLASH, "//", prefix=node.prefix)

tests/test_fix_classic_division.py

@@ -0,0 +1,33 @@
+from __future__ import absolute_import
+
+from utils import check_on_input
+
+
+CLASSIC_DIVISION = ("""\
+1 / 2
+""",
+"""\
+from __future__ import division
+1 // 2
+""")
+
+NEW_DIVISION = ("""\
+from __future__ import division
+1 / 2
+""",
+"""\
+from __future__ import division
+1 / 2
+""")
+
+
+def test_optional():
+    check_on_input(CLASSIC_DIVISION[0], CLASSIC_DIVISION[0])
+
+def test_fix_classic_division():
+    check_on_input(*CLASSIC_DIVISION,
+            extra_flags=['-f', 'libmodernize.fixes.fix_classic_division'])
+
+def test_new_division():
+    check_on_input(*NEW_DIVISION,
+            extra_flags=['-f', 'libmodernize.fixes.fix_classic_division'])