Fix wraps handing of missing attrs. (#251)

This is pretty-much a straight backport of Py3 implementations of update_wrapper and (privately) wraps.

Fixes #250 
Fixes #165

Co-authored-by: Benjamin Peterson <benjamin@python.org>

1 files changed, 25 insertions, 6 deletions

diff --git a/six.py b/six.py
index de1fcc5..d68d91c 100644
--- a/six.py
+++ b/six.py
@@ -808,13 +808,33 @@ if sys.version_info[:2] < (3, 3):
 _add_doc(reraise, """Reraise an exception.""")
 
 if sys.version_info[0:2] < (3, 4):
+    # This does exactly the same what the :func:`py3:functools.update_wrapper`
+    # function does on Python versions after 3.2. It sets the ``__wrapped__``
+    # attribute on ``wrapper`` object and it doesn't raise an error if any of
+    # the attributes mentioned in ``assigned`` and ``updated`` are missing on
+    # ``wrapped`` object.
+    def _update_wrapper(wrapper, wrapped,
+                        assigned=functools.WRAPPER_ASSIGNMENTS,
+                        updated=functools.WRAPPER_UPDATES):
+        for attr in assigned:
+            try:
+                value = getattr(wrapped, attr)
+            except AttributeError:
+                continue
+            else:
+                setattr(wrapper, attr, value)
+        for attr in updated:
+            getattr(wrapper, attr).update(getattr(wrapped, attr, {}))
+        wrapper.__wrapped__ = wrapped
+        return wrapper
+    _update_wrapper.__doc__ = functools.update_wrapper.__doc__
+
     def wraps(wrapped, assigned=functools.WRAPPER_ASSIGNMENTS,
               updated=functools.WRAPPER_UPDATES):
-        def wrapper(f):
-            f = functools.wraps(wrapped, assigned, updated)(f)
-            f.__wrapped__ = wrapped
-            return f
-        return wrapper
+        return functools.partial(_update_wrapper, wrapped=wrapped,
+                                 assigned=assigned, updated=updated)
+    wraps.__doc__ = functools.wraps.__doc__
+
 else:
     wraps = functools.wraps
 
@@ -919,7 +939,6 @@ def ensure_text(s, encoding='utf-8', errors='strict'):
         raise TypeError("not expecting type '%s'" % type(s))
 
 
-
 def python_2_unicode_compatible(klass):
     """
     A class decorator that defines __unicode__ and __str__ methods under Python 2.