Reduce number of false positives emitted by non-iterator-returned checker

By disabling checker for cases when there're multiple possible values infered
for node. This way we lose some of the inference power, but throw a lot less
false positives.

Fixes issue #695.

4 files changed, 27 insertions, 19 deletions

diff --git a/pylint/checkers/classes.py b/pylint/checkers/classes.py
index 3d9144d34..24b862fd7 100644
--- a/pylint/checkers/classes.py
+++ b/pylint/checkers/classes.py
@@ -1067,12 +1067,15 @@ class SpecialMethodsChecker(BaseChecker):
 
     def _check_iter(self, node):
         try:
-            infered = node.infer_call_result(node)
+            infered_values = list(node.infer_call_result(node))
         except astroid.InferenceError:
             return
-
-        if not all(map(self._is_iterator, infered)):
-            self.add_message('non-iterator-returned', node=node)
+        # cases when there're multiple values infered
+        # are skipped to reduce the number of false positives
+        if len(infered_values) == 1:
+            infered = infered_values[0]
+            if not self._is_iterator(infered):
+                self.add_message('non-iterator-returned', node=node)
 
 
 def _ancestors_to_call(klass_node, method='__init__'):
diff --git a/pylint/test/functional/non_iterator_returned.py b/pylint/test/functional/non_iterator_returned.py
index 804ceee7c..d2fa75804 100644
--- a/pylint/test/functional/non_iterator_returned.py
+++ b/pylint/test/functional/non_iterator_returned.py
@@ -56,6 +56,19 @@ class FifthGoodIterator(object):
     def __iter__(self):
         return IteratorClass
 
+class FileBasedIterator(object):
+    def __init__(self, path):
+        self.path = path
+        self.file = None
+
+    def __iter__(self):
+        if self.file is not None:
+            self.file.close()
+        self.file = open(self.path)
+        # self file has two infered values: None and <instance of 'file'>
+        # we don't want to emit error in this case
+        return self.file
+
 
 class FirstBadIterator(object):
     """ __iter__ returns a list """
@@ -80,11 +93,3 @@ class FourthBadIterator(object):
 
     def __iter__(self): # [non-iterator-returned]
         return ThirdBadIterator
-
-class FifthBadIterator(object):
-    """All branches should return an iterator."""
-
-    def __iter__(self): # [non-iterator-returned]
-        if self:
-            return 1
-        return SecondGoodIterator()
diff --git a/pylint/test/functional/non_iterator_returned.txt b/pylint/test/functional/non_iterator_returned.txt
index fe3db101d..fa1d5bec5 100644
--- a/pylint/test/functional/non_iterator_returned.txt
+++ b/pylint/test/functional/non_iterator_returned.txt
@@ -1,5 +1,4 @@
-non-iterator-returned:63:FirstBadIterator.__iter__:__iter__ returns non-iterator
-non-iterator-returned:69:SecondBadIterator.__iter__:__iter__ returns non-iterator
-non-iterator-returned:75:ThirdBadIterator.__iter__:__iter__ returns non-iterator
-non-iterator-returned:81:FourthBadIterator.__iter__:__iter__ returns non-iterator
-non-iterator-returned:87:FifthBadIterator.__iter__:__iter__ returns non-iterator
\ No newline at end of file
+non-iterator-returned:76:FirstBadIterator.__iter__:__iter__ returns non-iterator
+non-iterator-returned:82:SecondBadIterator.__iter__:__iter__ returns non-iterator
+non-iterator-returned:88:ThirdBadIterator.__iter__:__iter__ returns non-iterator
+non-iterator-returned:94:FourthBadIterator.__iter__:__iter__ returns non-iterator
diff --git a/tox.ini b/tox.ini
index d9fcff1d4..7c911da8b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,7 @@
 [tox]
 # official list is
 #envlist = py27, py32, py33, py34
-envlist = py27, py33, pylint
+envlist = py27, py34, pylint
 
 [testenv:pylint]
 deps =
@@ -14,5 +14,6 @@ commands = pylint -rn --rcfile={toxinidir}/pylintrc {envsitepackagesdir}/pylint
 deps =
   hg+https://bitbucket.org/logilab/astroid@master
   six
+  pudb
 commands = python -Wi -m unittest discover -s {envsitepackagesdir}/pylint/test/ -p {posargs:*test_*}.py
-changedir = {toxworkdir}
\ No newline at end of file
+changedir = {toxworkdir}