Add fix_nonzero fixer to rename and alias __nonzero__ to __bool__.

docs/fixers.rst

@@ -181,6 +181,12 @@ version of ``six`` is installed.
    .. seealso::
       :func:`six.with_metaclass`
 
+.. 2to3fixer:: nonzero
+
+   Changes all definitions of :func:`__nonzero__ <python2:__nonzero__>` to
+   :func:`__bool__ <python3:__bool__>`, adding an alias that maintains PY2
+   compatibility.
+
 .. 2to3fixer:: raise_six
 
    Changes ``raise E, V, T`` to ``six.reraise(E, V, T)``.

libmodernize/fixes/__init__.py

@@ -39,6 +39,7 @@
     'libmodernize.fixes.fix_int_long_tuple',
     'libmodernize.fixes.fix_map',
     'libmodernize.fixes.fix_metaclass',
+    'libmodernize.fixes.fix_nonzero',
     'libmodernize.fixes.fix_raise_six',
     'libmodernize.fixes.fix_unicode',
     'libmodernize.fixes.fix_unicode_type',

libmodernize/fixes/fix_nonzero.py

@@ -0,0 +1,72 @@
+"""Fixer for `__nonzero__` -> `__bool__`, adding an alias for PY2 compatibility.
+
+Based on Lib/lib2to3/fixes/fix_nonzero.py.
+
+"""
+# This is a derived work of Lib/lib2to3/fixes/fix_nonzero.py. That file
+# is under the copyright of the Python Software Foundation and licensed
+# under the Python Software Foundation License 2.
+#
+# Copyright notice:
+#
+#     2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
+#     2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020
+#     Python Software Foundation; All Rights Reserved.
+
+# Author: Collin Winter, James Bowman
+
+from __future__ import absolute_import
+from lib2to3 import fixer_base
+from lib2to3.fixer_util import Assign, Dot, find_indentation, Leaf, Name, Newline, Node, syms
+from lib2to3.pygram import token
+import libmodernize
+
+
+class FixNonzero(fixer_base.BaseFix):
+    BM_compatible = True
+
+    PATTERN = """
+    classdef< 'class' any+ ':'
+              suite< any*
+                     funcdef< 'def' name='__nonzero__'
+                              parameters< '(' NAME ')' > any+ >
+                     any* > >
+    """
+
+    def transform(self, node, results):
+        # Start by making the same transformation as lib2to3.fix_nonzero, purely
+        # renaming the method:
+
+        name = results["name"]
+        bool_funcdef = name.parent
+        new_name = Name("__bool__", prefix=name.prefix)
+        name.replace(new_name)
+
+        # Then, import six and add a conditional PY2-enabled function alias:
+
+        libmodernize.touch_import(None, u'six', node)
+
+        suite = bool_funcdef.parent
+        bool_funcdef_suite = bool_funcdef.children[-1]
+        old_dedent = bool_funcdef_suite.children[-1]
+        new_dedent = Leaf(token.DEDENT, '', prefix='\n' + find_indentation(bool_funcdef))
+        bool_funcdef_suite.children[-1].replace(new_dedent)
+
+        reassignment = Node(syms.suite, [
+            Newline(),
+            Leaf(token.INDENT,
+                 find_indentation(bool_funcdef.children[-1].children[1])),
+            Node(syms.simple_stmt,
+                 [Assign(Name('__nonzero__'), Name('__bool__')),
+                  Newline()]), old_dedent
+        ])
+
+        if_stmt = Node(syms.if_stmt, [
+            Name('if'),
+            Node(syms.power,
+                 [Name(' six'),
+                  Node(syms.trailer, [Dot(), Name('PY2')])]),
+            Leaf(token.COLON, ':'), reassignment
+        ])
+
+        suite.insert_child(suite.children.index(bool_funcdef) + 1, if_stmt)

tests/test_fix_nonzero.py

@@ -0,0 +1,111 @@
+from __future__ import absolute_import
+
+from utils import check_on_input
+
+
+NONZERO_DEF = ("""\
+class Foo:
+    def other(self):
+        return false
+
+    def __nonzero__(self):
+        return true
+
+    def another(self):
+        return false
+""", """\
+from __future__ import absolute_import
+import six
+class Foo:
+    def other(self):
+        return false
+
+    def __bool__(self):
+        return true
+
+    if six.PY2:
+        __nonzero__ = __bool__
+
+    def another(self):
+        return false
+""")
+
+NONZERO_DEF_2_SPACE_INDENT = ("""\
+class Foo:
+  def other(self):
+    return false
+
+  def __nonzero__(self):
+    return true
+
+  def another(self):
+    return false
+""", """\
+from __future__ import absolute_import
+import six
+class Foo:
+  def other(self):
+    return false
+
+  def __bool__(self):
+    return true
+
+  if six.PY2:
+    __nonzero__ = __bool__
+
+  def another(self):
+    return false
+""")
+
+MULTI_CLASS_NONZERO_DEF = ("""\
+class Foo:
+    def __nonzero__(self):
+        return true
+
+
+class Bar:
+    pass
+""", """\
+from __future__ import absolute_import
+import six
+class Foo:
+    def __bool__(self):
+        return true
+
+    if six.PY2:
+        __nonzero__ = __bool__
+
+
+class Bar:
+    pass
+""")
+
+INNER_CLASS_NONZERO_DEF = ("""\
+class Baz:
+    class Foo:
+        def __nonzero__(self):
+            return true
+""", """\
+from __future__ import absolute_import
+import six
+class Baz:
+    class Foo:
+        def __bool__(self):
+            return true
+
+        if six.PY2:
+            __nonzero__ = __bool__
+""")
+
+
+def test_nonzero_def():
+    check_on_input(*NONZERO_DEF)
+
+def test_nonzero_def_2_space_indent():
+    check_on_input(*NONZERO_DEF_2_SPACE_INDENT)
+
+def test_multi_class_nonzero_def():
+    check_on_input(*MULTI_CLASS_NONZERO_DEF)
+
+def test_inner_class_nonzero_def():
+    check_on_input(*INNER_CLASS_NONZERO_DEF)