Fix an 'unused-variable' false positive, where the variable is assigned through an import. Closes issue #196.

4 files changed, 67 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 0e005c4..390b374 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -36,6 +36,9 @@ ChangeLog for Pylint
     * Don't emit 'no-name-in-module' for ignored modules.
       Closes issue #223.
 
+    * Fix an 'unused-variable' false positive, where the variable is
+      assigned through an import. Closes issue #196.
+
 2014-04-30  --  1.2.1
     * Restore the ability to specify the init-hook option via the
       configuration file, which was accidentally broken in 1.2.0.
diff --git a/checkers/variables.py b/checkers/variables.py
index 6cbcdb6..94a8d6e 100644
--- a/checkers/variables.py
+++ b/checkers/variables.py
@@ -356,6 +356,10 @@ builtins. Remember that you should avoid to define new builtins when possible.'
         authorized_rgx = self.config.dummy_variables_rgx
         called_overridden = False
         argnames = node.argnames()
+        global_names = set()
+        for global_stmt in node.nodes_of_class(astroid.Global):
+            global_names.update(set(global_stmt.names))
+
         for name, stmts in not_consumed.iteritems():
             # ignore some special names specified by user configuration
             if authorized_rgx.match(name):
@@ -365,6 +369,23 @@ builtins. Remember that you should avoid to define new builtins when possible.'
             stmt = stmts[0]
             if isinstance(stmt, astroid.Global):
                 continue
+            if isinstance(stmt, (astroid.Import, astroid.From)):
+                # Detect imports, assigned to global statements.
+                if global_names:
+                    skip = False
+                    for import_name, import_alias in stmt.names:
+                        # If the import uses an alias, check only that.
+                        # Otherwise, check only the import name.
+                        if import_alias:
+                            if import_alias in global_names:
+                                skip = True
+                                break
+                        elif import_name in global_names:
+                            skip = True
+                            break
+                    if skip:
+                        continue
+
             # care about functions with unknown argument (builtins)
             if name in argnames:
                 if is_method:
@@ -412,7 +433,26 @@ builtins. Remember that you should avoid to define new builtins when possible.'
                     break
             else:
                 # global but no assignment
-                self.add_message('global-variable-not-assigned', args=name, node=node)
+                # Detect imports in the current frame, with the required
+                # name. Such imports can be considered assignments.
+                imports = frame.nodes_of_class((astroid.Import, astroid.From))
+                for import_node in imports:
+                    found = False
+                    for import_name, import_alias in import_node.names:
+                        # If the import uses an alias, check only that.
+                        # Otherwise, check only the import name.
+                        if import_alias:
+                            if import_alias == name:
+                                found = True
+                                break
+                        elif import_name and import_name == name:
+                            found = True
+                            break
+                    if found:
+                        break
+                else:
+                    self.add_message('global-variable-not-assigned',
+                                     args=name, node=node)
                 default_message = False
             if not assign_nodes:
                 continue
diff --git a/test/input/func_w0612.py b/test/input/func_w0612.py
index 57e139c..e871bb2 100644
--- a/test/input/func_w0612.py
+++ b/test/input/func_w0612.py
@@ -1,7 +1,8 @@
 """test unused variable
 """
-
+# pylint: disable=invalid-name, redefined-outer-name
 __revision__ = 0
+PATH = OS = collections = deque = None
 
 def function(matches):
     """"yo"""
@@ -20,3 +21,18 @@ def visit_if(self, node):
     self.inc_branch(branches)
     self.stmts += branches
 
+def test_global():
+    """ Test various assignments of global
+    variables through imports.
+    """
+    global PATH, OS, collections, deque
+    from os import path as PATH
+    import os as OS
+    import collections
+    from collections import deque
+    # make sure that these triggers unused-variable
+    from sys import platform
+    from sys import version as VERSION
+    import this
+    import re as RE
+
diff --git a/test/messages/func_w0612.txt b/test/messages/func_w0612.txt
index f1647a3..c81b4f9 100644
--- a/test/messages/func_w0612.txt
+++ b/test/messages/func_w0612.txt
@@ -1,2 +1,6 @@
-W:  8:function: Unused variable 'aaaa'
-W:  9:function: Unused variable 'index'
+W:  9:function: Unused variable 'aaaa'
+W: 10:function: Unused variable 'index'
+W: 34:test_global: Unused variable 'platform'
+W: 35:test_global: Unused variable 'VERSION'
+W: 36:test_global: Unused variable 'this'
+W: 37:test_global: Unused variable 'RE'