From e3aa096710619f7b4647b9656649f90b29fe6eba Mon Sep 17 00:00:00 2001
From: Claudiu Popa <pcmanticore@gmail.com>
Date: Thu, 26 Nov 2015 15:35:03 +0200
Subject: Added a new warning, 'unsupported-assignment-operation'

This is emitted when item assignment is tried on an object which doesn't
have this ability. Closes issue #591.
---
 pylint/checkers/typecheck.py | 41 +++++++++++++++++++++++++++++++++++------
 1 file changed, 35 insertions(+), 6 deletions(-)

(limited to 'pylint/checkers/typecheck.py')

diff --git a/pylint/checkers/typecheck.py b/pylint/checkers/typecheck.py
index 43b0bde..75cb193 100644
--- a/pylint/checkers/typecheck.py
+++ b/pylint/checkers/typecheck.py
@@ -38,7 +38,8 @@ from pylint.checkers.utils import (
     decorated_with, node_ignores_exception,
     is_iterable, is_mapping, supports_membership_test,
     is_comprehension, is_inside_abstract_class,
-    supports_subscript,
+    supports_getitem,
+    supports_setitem,
     safe_infer,
     has_known_bases)
 from pylint import utils
@@ -161,6 +162,10 @@ MSGS = {
               'unsubscriptable-object',
               "Emitted when a subscripted value doesn't support subscription"
               "(i.e. doesn't define __getitem__ method)"),
+    'E1137': ("%r does not support item assignment",
+              'unsupported-assignment-operation',
+              "Emitted when an object does not support item assignment "
+              "(i.e. doesn't define __setitem__ method)"),
     }
 
 # builtin sequence types in Python 2 and 3.
@@ -825,18 +830,42 @@ accessed. Python regular expressions are accepted.'}
         if operator in ['in', 'not in']:
             self._check_membership_test(right)
 
+    @staticmethod
+    def _is_subscript_store_context(node):
+        statement = node.statement()
+        if isinstance(statement, astroid.Assign):
+            for target in statement.targets:
+                if target is node or target.parent_of(node):
+                    return False
+        return True
+
     @check_messages('unsubscriptable-object')
     def visit_subscript(self, node):
         if isinstance(node.value, (astroid.ListComp, astroid.DictComp)):
             return
+
+        store_context = self._is_subscript_store_context(node)
         if isinstance(node.value, astroid.SetComp):
-            self.add_message('unsubscriptable-object',
-                             args=node.value.as_string(),
+            if store_context:
+                msg = 'unsubscriptable-object'
+            else:
+                msg = 'unsupported-assignment-operation'
+            self.add_message(msg, args=node.value.as_string(),
                              node=node.value)
-        infered = safe_infer(node.value)
-        if infered is None or infered is astroid.YES:
             return
-        if not supports_subscript(infered):
+
+        inferred = safe_infer(node.value)
+        if inferred is None or inferred is astroid.YES:
+            return
+
+        if not store_context:
+            if not supports_setitem(inferred):
+                self.add_message('unsupported-assignment-operation',
+                                 args=node.value.as_string(),
+                                 node=node.value)
+            return
+
+        if not supports_getitem(inferred):
             self.add_message('unsubscriptable-object',
                              args=node.value.as_string(),
                              node=node.value)
-- 
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