Fix a false positive with string formatting checker, when using keyword argument packing. Closes issue #288.

3 files changed, 22 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 4bef070..b5bea9a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -6,6 +6,9 @@ ChangeLog for Pylint
       encountering a string which uses only position-based arguments.
       Closes issue #285.
 
+    * Fix a false positive with string formatting checker, when using
+      keyword argument packing. Closes issue #288.
+
 2014-07-26  --  1.3.0
 
     * Allow hanging continued indentation for implicitly concatenated
diff --git a/checkers/strings.py b/checkers/strings.py
index a07482a..6f6f3bb 100644
--- a/checkers/strings.py
+++ b/checkers/strings.py
@@ -386,24 +386,30 @@ class StringMethodsChecker(BaseChecker):
                 key = 0
             if isinstance(key, int):
                 try:
-                    argument = utils.get_argument_from_call(node, key)
+                    argname = utils.get_argument_from_call(node, key)
                 except utils.NoSuchArgumentError:
                     continue
             else:
                 if key not in named:
                     continue
-                argument = named[key]
-            if argument in (astroid.YES, None):
+                argname = named[key]
+            if argname in (astroid.YES, None):
                 continue
             try:
-                argument = argument.infer().next()
+                argument = argname.infer().next()
             except astroid.InferenceError:
                 continue
             if not specifiers or argument is astroid.YES:
                 # No need to check this key if it doesn't
                 # use attribute / item access
                 continue
-
+            if argument.parent and isinstance(argument.parent, astroid.Arguments):
+                # Check to see if our argument is kwarg or vararg,
+                # and skip the check for this argument if so, because when inferring,
+                # astroid will return empty objects (dicts and tuples) and
+                # that can lead to false positives.
+                if argname.name in (argument.parent.kwarg, argument.parent.vararg):
+                    continue
             previous = argument
             parsed = []
             for is_attribute, specifier in specifiers:
diff --git a/test/input/func_string_format_py27.py b/test/input/func_string_format_py27.py
index 38eafd1..e2bfe12 100644
--- a/test/input/func_string_format_py27.py
+++ b/test/input/func_string_format_py27.py
@@ -78,3 +78,11 @@ def pprint_bad():
     print "{0.missing}".format(2)

     print "{0} {1} {2}".format(1, 2)

     print "{0} {1}".format(1, 2, 3)

+

+def good_issue288(*args, **kwargs):

+    """ Test that using kwargs does not emit a false

+    positive.

+    """

+    data = 'Hello John Doe {0[0]}'.format(args)

+    print data

+    return 'Hello {0[name]}'.format(kwargs)