Add some naive support for nonlocals

Author: dannysepler

pyflakes/checker.py

@@ -1854,7 +1854,7 @@ def ASSERT(self, node):
             self.report(messages.AssertTuple, node)
         self.handleChildren(node)
 
-    def GLOBAL(self, node):
+    def GLOBAL(self, node, assign_by_default=False):
         """
         Keep track of globals declarations.
         """
@@ -1866,7 +1866,7 @@ def GLOBAL(self, node):
 
             # One 'global' statement can bind multiple (comma-delimited) names.
             for node_name in node.names:
-                node_value = Assignment(node_name, node, assigned=False)
+                node_value = Assignment(node_name, node, assigned=assign_by_default)
 
                 # Remove UndefinedName messages already reported for this name.
                 self.messages = [
@@ -1882,7 +1882,11 @@ def GLOBAL(self, node):
                 for scope in self.scopeStack[global_scope_index + 1:]:
                     scope[node_name] = node_value
 
-    NONLOCAL = GLOBAL
+    def NONLOCAL(self, node):
+        for node_name in node.names:
+            if not any(node_name in scope for scope in self.scopeStack[:-1]):
+                self.report(messages.NoBindingForNonlocal, node, node_name)
+        self.GLOBAL(node, assign_by_default=True)
 
     def GENERATOREXP(self, node):
         self.pushScope(GeneratorScope)

pyflakes/messages.py

@@ -73,6 +73,14 @@ def __init__(self, filename, loc, name):
         self.message_args = (name,)
 
 
+class NoBindingForNonlocal(Message):
+    message = 'no binding for nonlocal %r found'
+
+    def __init__(self, filename, loc, name):
+        Message.__init__(self, filename, loc)
+        self.message_args = (name,)
+
+
 class DoctestSyntaxError(Message):
     message = 'syntax error in doctest'
 

pyflakes/test/test_undefined_names.py

@@ -327,6 +327,33 @@ def a():
         fu
         ''', m.UndefinedName)
 
+    def test_scope_defined_nonlocal(self):
+        """
+        If a "nonlocal" is declared in a previous scope,
+        it is defined
+        """
+        self.flakes('''
+        def a():
+            fu = 1
+            def b():
+                nonlocal fu
+                fu
+        ''')
+
+    def test_scope_undefined_nonlocal(self):
+        """
+        If a "nonlocal" is never given a value, it is undefined
+        """
+        self.flakes('''
+        def a():
+            nonlocal fu
+        ''', m.NoBindingForNonlocal)
+
+        self.flakes('''
+        def a():
+            nonlocal fu, bar
+        ''', m.NoBindingForNonlocal, m.NoBindingForNonlocal)
+
     def test_definedByGlobalMultipleNames(self):
         """
         "global" can accept multiple names.