Deserialize by using __new__ instead of constructor if possible

Exception to IOError is because this built-in exception is assigning
internal myerrno attribute in __init__ constructor and cannot be changed
from Python code.

Fixes: #65

Signed-off-by: Oldřich Jedlička <[email protected]>

Author: oldium

src/tblib/pickling_support.py

@@ -1,6 +1,6 @@
 import copyreg
 from functools import partial
-from types import TracebackType
+from types import BuiltinFunctionType, TracebackType
 
 from . import Frame
 from . import Traceback
@@ -22,6 +22,19 @@ def pickle_traceback(tb, *, get_locals=None):
     )
 
 
+def unpickle_builtin_exception(func, args, cause, tb, context, suppress_context, notes):
+    inst = func.__new__(func)
+    if args is not None:
+        inst.args = args
+    inst.__cause__ = cause
+    inst.__traceback__ = tb
+    inst.__context__ = context
+    inst.__suppress_context__ = suppress_context
+    if notes is not None:
+        inst.__notes__ = notes
+    return inst
+
+
 # Note: Older versions of tblib will generate pickle archives that call unpickle_exception() with
 # fewer arguments. We assign default values to some of the arguments to support this.
 def unpickle_exception(func, args, cause, tb, context=None, suppress_context=False, notes=None):
@@ -49,8 +62,12 @@ def pickle_exception(obj):
     assert isinstance(rv, tuple)
     assert len(rv) >= 2
 
+    use_builtin = isinstance(obj.__reduce_ex__, BuiltinFunctionType) and \
+                  isinstance(obj.__reduce__, BuiltinFunctionType) and \
+                  not isinstance(obj, IOError)
+
     return (
-        unpickle_exception,
+        unpickle_builtin_exception if use_builtin else unpickle_exception,
         rv[:2]
         + (
             obj.__cause__,