Refactoring: extract method ModuleGraph.warn()

Strictly speaking this also changes observable behaviour: duplicate "bad
file name extension" warnings will not be repeated.  I'd say that's a
bugfix :)

findimports.py

@@ -48,7 +48,7 @@
         findimports.py foo.importcache -d -N -c -p -l 2 > graph2.dot
 
 
-Copyright (c) 2003--2014 Marius Gedminas <marius@pov.lt>
+Copyright (c) 2003--2015 Marius Gedminas <marius@pov.lt>
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -384,6 +384,15 @@ def __init__(self):
         self.path = sys.path
         self._module_cache = {}
         self._warned_about = set()
+        self._stderr = sys.stderr
+
+    def warn(self, about, message, *args):
+        if about in self._warned_about:
+            return
+        if args:
+            message = message % args
+        print >> self._stderr, message
+        self._warned_about.add(about)
 
     def parsePathname(self, pathname):
         """Parse one or more source files.
@@ -440,7 +449,7 @@ def filenameToModname(self, filename):
                 filename = filename[:-len(ext)]
                 break
         else:
-            print >> sys.stderr, "%s: unknown file name extension" % filename
+            self.warn(filename, '%s: unknown file name extension', filename)
         filename = os.path.abspath(filename)
         elements = filename.split(os.path.sep)
         modname = []
@@ -480,10 +489,7 @@ def findModuleOfName(self, dotted_name, level, filename, extrapath=None):
             if candidate:
                 return candidate
             name = name[:name.rfind('.')]
-        if dotted_name not in self._warned_about:
-            print >> sys.stderr, ("%s: could not find %s"
-                                  % (filename, dotted_name))
-            self._warned_about.add(dotted_name)
+        self.warn(dotted_name, '%s: could not find %s', filename, dotted_name)
         return dotted_name
 
     def isModule(self, dotted_name, extrapath=None):
@@ -515,10 +521,7 @@ def isModule(self, dotted_name, extrapath=None):
                 try:
                     zf = zipfile.ZipFile(dir)
                 except zipfile.BadZipfile:
-                    if dir not in self._warned_about:
-                        print >> sys.stderr, ("%s: not a directory or zip file"
-                                              % dir)
-                        self._warned_about.add(dir)
+                    self.warn(dir, "%s: not a directory or zip file", dir)
                     continue
                 names = zf.namelist()
                 for ext in ('.py', '.so', '.dll'):

tests.py

@@ -1,10 +1,32 @@
 import unittest
+from cStringIO import StringIO
 
 import findimports
 
 
 class TestModuleGraph(unittest.TestCase):
 
+    def setUp(self):
+        self.warnings = []
+
+    def warn(self, about, message, *args):
+        if args:
+            message = message % args
+        self.warnings.append(message)
+
+    def test_warn(self):
+        mg = findimports.ModuleGraph()
+        mg._stderr = StringIO()
+        mg.warn('foo', 'no module %s', 'foo')
+        self.assertEqual(mg._stderr.getvalue(), 'no module foo\n')
+
+    def test_warn_suppresses_duplicates(self):
+        mg = findimports.ModuleGraph()
+        mg._stderr = StringIO()
+        mg.warn('foo', 'no module foo')
+        mg.warn('foo', 'no module foo (again)')
+        self.assertEqual(mg._stderr.getvalue(), 'no module foo\n')
+
     def test_isModule(self):
         mg = findimports.ModuleGraph()
         self.assertTrue(mg.isModule('os'))