issue #310: fix test failures, teach old import method new tricks

- don't try anything unless something really lives in sys.modules by
  that name
- non-ASCII files are possible
- the unimportable thing might be an extension module, we don't want
  that

mitogen/master.py

@@ -459,6 +459,11 @@ class ModuleFinder(object):
         insane) parent package. Required for older versions of
         ansible.compat.six and plumbum.colors.
         """
+        if fullname not in sys.modules:
+            # Don't attempt this unless a module really exists in sys.modules,
+            # else we could return junk.
+            return
+
         pkgname, _, modname = fullname.rpartition('.')
         pkg = sys.modules.get(pkgname)
         if pkg is None or not hasattr(pkg, '__file__'):
@@ -467,7 +472,21 @@ class ModuleFinder(object):
         pkg_path = os.path.dirname(pkg.__file__)
         try:
             fp, path, ext = imp.find_module(modname, [pkg_path])
-            return path, fp.read().encode('utf-8'), False
+            try:
+                path = self._py_filename(path)
+                if not path:
+                    fp.close()
+                    return
+
+                source = fp.read()
+            finally:
+                fp.close()
+
+            if isinstance(source, mitogen.core.UnicodeType):
+                # get_source() returns "string" according to PEP-302, which was
+                # reinterpreted for Python 3 to mean a Unicode string.
+                source = source.encode('utf-8')
+            return path, source, False
         except ImportError:
             e = sys.exc_info()[1]
             LOG.debug('imp.find_module(%r, %r) -> %s', modname, [pkg_path], e)
@@ -491,6 +510,7 @@ class ModuleFinder(object):
         for method in self.get_module_methods:
             tup = method(self, fullname)
             if tup:
+                #LOG.debug('%r returned %r', method, tup)
                 break
         else:
             tup = None, None, None

tests/data/pkg_like_plumbum/colors.py

@@ -1,7 +1,11 @@
 
+# coding=utf-8
+
 import sys
 
 
+# £
+
 class EvilObject(object):
     """
     Wild cackles! I have come to confuse perplex your importer with rainbows!

tests/module_finder_test.py

@@ -133,8 +133,8 @@ class GetModuleViaParentEnumerationTest(testlib.TestCase):
         self.assertEquals(path,
             testlib.data_path('pkg_like_plumbum/colors.py'))
 
-        s = open(testlib.data_path('pkg_like_plumbum/colors.py')).read()
-        self.assertEquals(mitogen.core.to_text(src), s)
+        s = open(testlib.data_path('pkg_like_plumbum/colors.py'), 'rb').read()
+        self.assertEquals(src, s)
         self.assertFalse(is_pkg)