Improve 'global' statement support.

Add declared globals to each scope in the scope stack to avoid
erroneous UndefinedName errors when they are loaded.

3 files changed, 53 insertions, 4 deletions

diff --git a/pyflakes/checker.py b/pyflakes/checker.py
index df2f907..de7c6f8 100644
--- a/pyflakes/checker.py
+++ b/pyflakes/checker.py
@@ -678,8 +678,30 @@ class Checker(object):
         """
         Keep track of globals declarations.
         """
-        if isinstance(self.scope, FunctionScope):
-            self.scope.globals.update(node.names)
+        # In doctests, the global scope is an anonymous function at index 1.
+        global_scope_index = 1 if self.withDoctest else 0
+        global_scope = self.scopeStack[global_scope_index]
+
+        # Ignore 'global' statement in global scope.
+        if self.scope is not global_scope:
+
+            # One 'global' statement can bind multiple (comma-delimited) names.
+            for node_name in node.names:
+                node_value = Assignment(node_name, node)
+
+                # Remove UndefinedName messages already reported for this name.
+                self.messages = [
+                    m for m in self.messages if not
+                    isinstance(m, messages.UndefinedName) and not
+                    m.message_args[0] == node_name]
+
+                # Bind name to global scope if it doesn't exist already.
+                global_scope.setdefault(node_name, node_value)
+
+                # Bind name to non-global scopes, but as already "used".
+                node_value.used = True
+                for scope in self.scopeStack[global_scope_index + 1:]:
+                    scope[node_name] = node_value
 
     NONLOCAL = GLOBAL
 
diff --git a/pyflakes/test/test_imports.py b/pyflakes/test/test_imports.py
index 389ebbf..077a728 100644
--- a/pyflakes/test/test_imports.py
+++ b/pyflakes/test/test_imports.py
@@ -505,11 +505,26 @@ class Test(TestCase):
         ''')
 
     def test_usedInGlobal(self):
+        """
+        A 'global' statement shadowing an unused import should not prevent it
+        from being reported.
+        """
         self.flakes('''
         import fu
         def f(): global fu
         ''', m.UnusedImport)
 
+    def test_usedAndGlobal(self):
+        """
+        A 'global' statement shadowing a used import should not cause it to be
+        reported as unused.
+        """
+        self.flakes('''
+            import foo
+            def f(): global foo
+            def g(): foo.is_used()
+        ''')
+
     @skipIf(version_info >= (3,), 'deprecated syntax')
     def test_usedInBackquote(self):
         self.flakes('import fu; `fu`')
diff --git a/pyflakes/test/test_undefined_names.py b/pyflakes/test/test_undefined_names.py
index 67c3f1f..faaaf8c 100644
--- a/pyflakes/test/test_undefined_names.py
+++ b/pyflakes/test/test_undefined_names.py
@@ -3,7 +3,7 @@ from _ast import PyCF_ONLY_AST
 from sys import version_info
 
 from pyflakes import messages as m, checker
-from pyflakes.test.harness import TestCase, skip, skipIf
+from pyflakes.test.harness import TestCase, skipIf
 
 
 class Test(TestCase):
@@ -92,7 +92,6 @@ class Test(TestCase):
             bar; baz
         ''')
 
-    @skip("todo")
     def test_definedByGlobal(self):
         """
         "global" can make an otherwise undefined name in another function
@@ -102,6 +101,19 @@ class Test(TestCase):
         def a(): global fu; fu = 1
         def b(): fu
         ''')
+        self.flakes('''
+        def c(): bar
+        def b(): global bar; bar = 1
+        ''')
+
+    def test_definedByGlobalMultipleNames(self):
+        """
+        "global" can accept multiple names.
+        """
+        self.flakes('''
+        def a(): global fu, bar; fu = 1; bar = 2
+        def b(): fu; bar
+        ''')
 
     def test_globalInGlobalScope(self):
         """