Look for __init__ instead of __new__ in _determine_callable_obj if __new__ comes from builtins.

Since the __new__ comes from builtins, it will not have attached any
information regarding what parameters it expects, so the check
will be useless. Retrieving __init__ in that case will at least
detect a couple of false negatives. Closes issue #429.

4 files changed, 24 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 4c0d67a..025e922 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -57,6 +57,14 @@ ChangeLog for Pylint
 
     * Provide some hints for the bad-builtin message. Closes issue #522.
 
+    * When checking for invalid arguments to a callable, in typecheck.py,
+      look up for the __init__ in case the found __new__ comes from builtins.
+      
+      Since the __new__ comes from builtins, it will not have attached any
+      information regarding what parameters it expects, so the check
+      will be useless. Retrieving __init__ in that case will at least
+      detect a couple of false negatives. Closes issue #429. 
+
 
 2015-03-14 -- 1.4.3
 
diff --git a/pylint/checkers/typecheck.py b/pylint/checkers/typecheck.py
index 58ce4be..ef3b799 100644
--- a/pylint/checkers/typecheck.py
+++ b/pylint/checkers/typecheck.py
@@ -103,14 +103,18 @@ def _determine_callable(callable_obj):
     elif isinstance(callable_obj, astroid.Class):
         # Class instantiation, lookup __new__ instead.
         # If we only find object.__new__, we can safely check __init__
-        # instead.
+        # instead. If __new__ belongs to builtins, then we look
+        # again for __init__ in the locals, since we won't have
+        # argument information for the builtin __new__ function.
         try:
             # Use the last definition of __new__.
             new = callable_obj.local_attr('__new__')[-1]
         except astroid.NotFoundError:
             new = None
 
-        if not new or new.parent.scope().name == 'object':
+        from_object = new and new.parent.scope().name == 'object'
+        from_builtins = new and new.root().name == BUILTINS
+        if not new or from_object or from_builtins:
             try:
                 # Use the last definition of __init__.
                 callable_obj = callable_obj.local_attr('__init__')[-1]
@@ -122,7 +126,7 @@ def _determine_callable(callable_obj):
 
         if not isinstance(callable_obj, astroid.Function):
             raise ValueError
-        # both have an extra implicit 'cls'/'self' argument.
+        # both have an extra implicit 'cls'/'self' argument.        
         return callable_obj, 1, 'constructor'
     else:
         raise ValueError
diff --git a/pylint/test/functional/ctor_arguments.py b/pylint/test/functional/ctor_arguments.py
index 7dc0a09..f052831 100644
--- a/pylint/test/functional/ctor_arguments.py
+++ b/pylint/test/functional/ctor_arguments.py
@@ -76,3 +76,10 @@ class ClassWithMeta(with_metaclass(Metaclass)):
     pass
 
 ClassWithMeta()
+
+
+class BuiltinExc(Exception):
+    def __init__(self, val=True):
+        self.val = val
+
+BuiltinExc(42, 24, badarg=1) # [too-many-function-args,unexpected-keyword-arg]
diff --git a/pylint/test/functional/ctor_arguments.txt b/pylint/test/functional/ctor_arguments.txt
index 85cf139..817e805 100644
--- a/pylint/test/functional/ctor_arguments.txt
+++ b/pylint/test/functional/ctor_arguments.txt
@@ -15,3 +15,5 @@ too-many-function-args:60::Too many positional arguments for constructor call
 too-many-function-args:63::Too many positional arguments for constructor call
 no-value-for-parameter:64::No value for argument 'first_argument' in constructor call
 unexpected-keyword-arg:64::Unexpected keyword argument 'one' in constructor call
+too-many-function-args:85::Too many positional arguments for constructor call
+unexpected-keyword-arg:85::Unexpected keyword argument 'badarg' in constructor call