Global variables must be assigned to be used

pyflakes/checker.py

@@ -250,10 +250,11 @@ class Binding:
                 the node that this binding was last used.
     """
 
-    def __init__(self, name, source):
+    def __init__(self, name, source, *, assigned=True):
         self.name = name
         self.source = source
         self.used = False
+        self.assigned = assigned
 
     def __str__(self):
         return self.name
@@ -1007,6 +1008,12 @@ def addBinding(self, node, value):
                 break
         existing = scope.get(value.name)
 
+        global_scope = self.scopeStack[-1]
+        if (existing and global_scope.get(value.name) == existing and
+                not existing.assigned):
+            # make sure the variable is in the global scope before setting as assigned
+            existing.assigned = True
+
         if (existing and not isinstance(existing, Builtin) and
                 not self.differentForks(node, existing.source)):
 
@@ -1089,6 +1096,10 @@ def handleNodeLoad(self, node):
                     continue
 
             binding = scope.get(name, None)
+
+            if binding and binding.assigned is False:
+                self.report(messages.UndefinedName, node, name)
+
             if isinstance(binding, Annotation) and not self._in_postponed_annotation:
                 scope[name].used = True
                 continue
@@ -1159,12 +1170,19 @@ def handleNodeStore(self, node):
                     continue
                 # if the name was defined in that scope, and the name has
                 # been accessed already in the current scope, and hasn't
-                # been declared global
+                # been assigned globally
                 used = name in scope and scope[name].used
                 if used and used[0] is self.scope and name not in self.scope.globals:
                     # then it's probably a mistake
                     self.report(messages.UndefinedLocal,
                                 scope[name].used[1], name, scope[name].source)
+
+                    # and remove UndefinedName messages already reported for this name
+                    self.messages = [
+                        m for m in self.messages if not
+                        isinstance(m, messages.UndefinedName) or
+                        m.message_args[0] != name]
+
                     break
 
         parent_stmt = self.getParent(node)
@@ -1836,7 +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.
         """
@@ -1848,11 +1866,9 @@ 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)
+                node_value = Assignment(node_name, node, assigned=assign_by_default)
 
                 # Remove UndefinedName messages already reported for this name.
-                # TODO: if the global is not used in this scope, it does not
-                # become a globally defined name.  See test_unused_global.
                 self.messages = [
                     m for m in self.messages if not
                     isinstance(m, messages.UndefinedName) or
@@ -1866,7 +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

@@ -298,6 +298,62 @@ def c(): bar
         def b(): global bar; bar = 1
         ''')
 
+    def test_unassigned_global_is_undefined(self):
+        """
+        If a "global" is never given a value, it is undefined
+        """
+        self.flakes('''
+        def a():
+            global fu
+            fu
+        ''', m.UndefinedName)
+
+        self.flakes('''
+        global fu
+        fu
+        ''', m.UndefinedName)
+
+    def test_scope_defined_global(self):
+        """
+        If a "global" is defined inside of a function only,
+        outside of the function it is undefined
+        """
+        self.flakes('''
+        global fu
+        def a():
+            fu = 1
+            fu
+        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.