Merge pull request h5py#399 from andrewcollette/issue_367

andrewcollette · andrewcollette · commit 1e10542c92ca · 2014-02-13T16:10:13.000-07:00
Allow opening readonly files with mode==None
diff --git a/h5py/_hl/files.py b/h5py/_hl/files.py
@@ -83,22 +83,37 @@ def make_fid(name, mode, userblock_size, fapl, fcpl=None):
         fid = h5f.create(name, h5f.ACC_EXCL, fapl=fapl, fcpl=fcpl)
     elif mode == 'w':
         fid = h5f.create(name, h5f.ACC_TRUNC, fapl=fapl, fcpl=fcpl)
-    elif mode == 'a' or mode is None:
+    elif mode == 'a':
+        # Open in append mode (read/write).
+        # If that fails, create a new file only if it won't clobber an
+        # existing one (ACC_EXCL)
         try:
             fid = h5f.open(name, h5f.ACC_RDWR, fapl=fapl)
-            try:
-                existing_fcpl = fid.get_create_plist()
-                if (userblock_size is not None and
-                        existing_fcpl.get_userblock() != userblock_size):
-                    raise ValueError("Requested userblock size (%d) does not match that of existing file (%d)" % (userblock_size, existing_fcpl.get_userblock()))
-            except:
-                fid.close()
-                raise
         except IOError:
             fid = h5f.create(name, h5f.ACC_EXCL, fapl=fapl, fcpl=fcpl)
+    elif mode is None:
+        # Try to open in append mode (read/write).
+        # If that fails, try readonly, and finally create a new file only
+        # if it won't clobber an existing file (ACC_EXCL).
+        try:
+            fid = h5f.open(name, h5f.ACC_RDWR, fapl=fapl)
+        except IOError:
+            try:
+                fid = h5f.open(name, h5f.ACC_RDONLY, fapl=fapl)
+            except IOError:
+                fid = h5f.create(name, h5f.ACC_EXCL, fapl=fapl, fcpl=fcpl)
     else:
         raise ValueError("Invalid mode; must be one of r, r+, w, w-, a")
 
+    try:
+        if userblock_size is not None:
+            existing_fcpl = fid.get_create_plist()
+            if existing_fcpl.get_userblock() != userblock_size:
+                raise ValueError("Requested userblock size (%d) does not match that of existing file (%d)" % (userblock_size, existing_fcpl.get_userblock()))
+    except:
+        fid.close()
+        raise
+
     return fid
 
 
diff --git a/h5py/tests/test_file.py b/h5py/tests/test_file.py
@@ -15,7 +15,7 @@
 
 from __future__ import with_statement
 
-import os
+import os, stat
 
 from .common import ut, TestCase, unicode_filenames
 from h5py.highlevel import File
@@ -29,6 +29,30 @@ class TestFileOpen(TestCase):
         Feature: Opening files with Python-style modes.
     """
 
+    def test_default(self):
+        """ Default semantics in the presence or absence of a file """
+        fname = self.mktemp()
+
+        # No existing file; create a new file and open RW
+        with File(fname) as f:
+            self.assertTrue(f)
+            self.assertEqual(f.mode, 'r+')
+
+        # Existing readonly file; open read-only
+        os.chmod(fname, stat.S_IREAD)
+        try:
+            with File(fname) as f:
+                self.assertTrue(f)
+                self.assertEqual(f.mode, 'r')
+        finally:
+            os.chmod(fname, stat.S_IWRITE)
+
+        # File exists but is not HDF5; raise IOError
+        with open(fname, 'wb') as f:
+            f.write(b'\x00')
+        with self.assertRaises(IOError):
+            File(fname)
+        
     def test_create(self):
         """ Mode 'w' opens file in overwrite mode """
         fname = self.mktemp()
