Changes after review by jmcgeheeiv

- added example test
- fixed documentation and formatting

CHANGES.md

@@ -4,8 +4,11 @@ The release versions are PyPi releases.
 ## Version 3.2 (as yet unreleased)
 
 #### New Features
- * Added possibility to add lazily read real files to fake filesystem
- * Added the CHANGES.md release notes to the release manifest
+  * Added new methods to `fake_filesystem.FakeFilesystem` that make real files 
+  and directories appear within the fake file system: 
+    `AddRealFile()`, `AddRealDirectory()` and `AddRealPaths()`
+
+File contents are read from the real file system only when needed. * Added the CHANGES.md release notes to the release manifest
 
 #### Fixes
  * `pathlib.glob()` incorrectly handled case under MacOS (#167)

example.py

@@ -132,5 +132,10 @@ def rm_tree(path):
     shutil.rmtree(path)
 
 def scandir(path):
-    """Returns a list of directory entries for the given path."""
+    """Return a list of directory entries for the given path."""
     return list(os.scandir(path))
+
+def file_contents(path):
+    """Return the contents of the given path as byte array."""
+    with open(path, 'rb') as f:
+        return f.read()

example_test.py

@@ -30,6 +30,8 @@
 import os
 import sys
 
+from pyfakefs.fake_filesystem_unittest import REAL_OPEN
+
 if sys.version_info < (2, 7):
     import unittest2 as unittest
 else:
@@ -135,13 +137,22 @@ def test_scandir(self):
         self.fs.CreateFile('/linktest/linked')
         self.fs.CreateLink('/test/linked_file', '/linktest/linked')
 
-        entries = sorted(os.scandir('/test'), key=lambda e: e.name)
+        entries = sorted(example.scandir('/test'), key=lambda e: e.name)
         self.assertEqual(3, len(entries))
         self.assertEqual('linked_file', entries[1].name)
         self.assertTrue(entries[0].is_dir())
         self.assertTrue(entries[1].is_symlink())
         self.assertTrue(entries[2].is_file())
 
+    def test_real_file_access(self):
+        """Test `example.file_contents()` for a real file after adding it using `AddRealFile()`."""
+        real_file = __file__
+        with REAL_OPEN(real_file, 'rb') as f:
+            real_contents = f.read()
+        self.assertRaises(IOError, example.file_contents, real_file)
+        self.fs.AddRealFile(real_file)
+        self.assertEqual(example.file_contents(real_file), real_contents)
+
 
 if __name__ == "__main__":
     unittest.main()

pyfakefs/fake_filesystem.py

@@ -196,7 +196,7 @@ def __init__(self, name, st_mode=stat.S_IFREG | PERM_DEF_FILE,
         self.name = name
         self.st_mode = st_mode
         self._byte_contents = self._EncodeContents(contents, encoding)
-        self.st_size = len(self._byte_contents) if self._byte_contents else 0
+        self.st_size = len(self._byte_contents) if self._byte_contents is not None else 0
         self.filesystem = filesystem
         self.epoch = 0
         self._st_ctime = time.time()  # times are accessed through properties
@@ -834,7 +834,7 @@ def GetOpenFile(self, file_des):
         if not isinstance(file_des, int):
             raise TypeError('an integer is required')
         if (file_des >= len(self.open_files) or
-                    self.open_files[file_des] is None):
+                self.open_files[file_des] is None):
             raise OSError(errno.EBADF, 'Bad file descriptor', file_des)
         return self.open_files[file_des]
 
@@ -897,7 +897,7 @@ def CollapsePath(self, path):
                 continue
             if component == '..':
                 if collapsed_path_components and (
-                            collapsed_path_components[-1] != '..'):
+                        collapsed_path_components[-1] != '..'):
                     # Remove an up-reference: directory/..
                     collapsed_path_components.pop()
                     continue
@@ -929,7 +929,7 @@ def NormalizeCase(self, path):
         for component in path_components:
             dir_name, current_dir = self._DirectoryContent(current_dir, component)
             if current_dir is None or (
-                            current_dir._byte_contents is None and current_dir.st_size == 0):
+                    current_dir._byte_contents is None and current_dir.st_size == 0):
                 return path
             normalized_components.append(dir_name)
         normalized_path = self.path_separator.join(normalized_components)
@@ -1014,7 +1014,7 @@ def SplitDrive(self, path):
                 # UNC path handling is here since Python 2.7.8, back-ported from Python 3
                 if sys.version_info >= (2, 7, 8):
                     if (path[0:2] == self.path_separator * 2) and (
-                                path[2:3] != self.path_separator):
+                            path[2:3] != self.path_separator):
                         # UNC path handling - splits off the mount point instead of the drive
                         sep_index = path.find(self.path_separator, 2)
                         if sep_index == -1: