Prefer posixpath to os.path

To ensure that the memory fake filesystem works uniformly
across distributions prefer to use the posixpath module
which always works with '/' and friends instead of the
os.path and os.path.sep and friends which may vary depending
on operating system used.

Since we have tested with the usage of '/' we might as well
just restrict to that; and avoid the cross operating system
issues that may pop up when using this fake filesystem.

In general isolating one self from the operating system specifics
is IMHO preferable for this; as it avoids edge cases that we
don't care about.

Change-Id: I3f61f380e1bcb131bc42b627adf9dfe8a7f2d992

taskflow/persistence/backends/impl_memory.py

@@ -17,7 +17,7 @@
 
 import contextlib
 import copy
-import os
+import posixpath as pp
 
 from taskflow import exceptions as exc
 from taskflow.persistence import path_based
@@ -29,14 +29,14 @@ class FakeFilesystem(object):
     """An in-memory filesystem-like structure."""
 
     #: Root path of the in-memory filesystem.
-    root_path = os.sep
+    root_path = pp.sep
 
     @classmethod
     def _normpath(cls, path):
         if not path.startswith(cls.root_path):
             raise ValueError("This filesystem can only normalize absolute"
                              " paths: '%s' is not valid" % path)
-        return os.path.normpath(path)
+        return pp.normpath(path)
 
     def __init__(self, deep_copy=True):
         self._root = tree.Node(self.root_path, value=None)
@@ -98,11 +98,11 @@ class FakeFilesystem(object):
             # split correctly:
             #
             # >>> path = "/"
-            # path.split(os.sep)
+            # path.split(pp.sep)
             # ['', '']
             parts = []
         else:
-            parts = path.split(os.sep)[1:]
+            parts = path.split(pp.sep)[1:]
         if include_root:
             parts.insert(0, self._root.item)
         for piece in parts:
@@ -120,7 +120,7 @@ class FakeFilesystem(object):
     def symlink(self, src_path, dest_path):
         dest_path = self._normpath(dest_path)
         src_path = self._normpath(src_path)
-        dirname, basename = os.path.split(dest_path)
+        dirname, basename = pp.split(dest_path)
         parent_node = self._fetch_node(dirname)
         child_node = parent_node.find(basename,
                                       only_direct=True,
@@ -140,7 +140,7 @@ class FakeFilesystem(object):
             item_node = self._fetch_node(path)
             item_node.metadata.update(value=value)
         except exc.NotFound:
-            dirname, basename = os.path.split(path)
+            dirname, basename = pp.split(path)
             parent_node = self._fetch_node(dirname)
             parent_node.add(tree.Node(basename, value=value))
 
@@ -159,7 +159,7 @@ class MemoryBackend(path_based.PathBasedBackend):
     def __init__(self, conf=None):
         super(MemoryBackend, self).__init__(conf)
         if self._path is None:
-            self._path = os.sep
+            self._path = pp.sep
         self.memory = FakeFilesystem(deep_copy=self._conf.get('deep_copy',
                                                               True))
         self.lock = lock_utils.ReaderWriterLock()
@@ -191,7 +191,7 @@ class Connection(path_based.PathBasedConnection):
                 raise exc.StorageFailure("Storage backend internal error", e)
 
     def _join_path(self, *parts):
-        return os.path.join(*parts)
+        return pp.join(*parts)
 
     def _get_item(self, path):
         with self._memory_lock():