Be more cautious open creating a file when the old one doesn't exist.

Workaround for bug in Python versions upto and including 2.1.3.  If
the interpreter was builtin without large file support but the
platform had it, os.path.exists() would return false for large files.
The fix is to try to open the file first, and decide whether to create
a new file based on errno.

(Only the two of the last three chunks of the diff affect this
behavior.)

Also cleanup imports and add some whitespace between arguments to func
calls.

src/ZODB/FileStorage.py

@@ -115,31 +115,37 @@
 #   may have a back pointer to a version record or to a non-version
 #   record.
 #
-__version__='$Revision: 1.93 $'[11:-2]
+__version__='$Revision: 1.94 $'[11:-2]
 
-import struct, time, os, string, base64, sys
-from struct import pack, unpack
-import POSException
-from POSException import UndoError, POSKeyError
-from TimeStamp import TimeStamp
-from lock_file import lock_file
-from utils import t32, p64, U64, cp
-from zLOG import LOG, BLATHER, WARNING, ERROR, PANIC, register_subsystem
-register_subsystem('ZODB FS')
-import BaseStorage
+import base64
 from cPickle import Pickler, Unpickler, loads
-import ConflictResolution
+import errno
+import os
+import struct
+import sys
+import time
+from types import StringType
+from struct import pack, unpack
 
 try:
-    from fsIndex import fsIndex
+    from posix import fsync
+except:
+    fsync = None
+
+from ZODB import BaseStorage, ConflictResolution, POSException
+from ZODB.POSException import UndoError, POSKeyError
+from ZODB.TimeStamp import TimeStamp
+from ZODB.lock_file import lock_file
+from ZODB.utils import t32, p64, U64, cp
+
+try:
+    from ZODB.fsIndex import fsIndex
 except ImportError:
     def fsIndex():
         return {}
 
-try: from posix import fsync
-except: fsync=None
-
-from types import StringType
+from zLOG import LOG, BLATHER, WARNING, ERROR, PANIC, register_subsystem
+register_subsystem('ZODB FS')
 
 z64='\0'*8
 # constants to support various header sizes
@@ -148,17 +154,20 @@ DATA_HDR_LEN = 42
 DATA_VERSION_HDR_LEN = 58
 
 def warn(message, *data):
-    LOG('ZODB FS',WARNING, "%s  warn: %s\n" % (packed_version, (message % data)))
+    LOG('ZODB FS', WARNING, "%s  warn: %s\n" % (packed_version,
+                                                (message % data)))
 
 def error(message, *data):
-    LOG('ZODB FS',ERROR,"%s ERROR: %s\n" % (packed_version, (message % data)))
+    LOG('ZODB FS', ERROR, "%s ERROR: %s\n" % (packed_version,
+                                              (message % data)))
 
 def nearPanic(message, *data):
-    LOG('ZODB FS',PANIC,"%s ERROR: %s\n" % (packed_version, (message % data)))
+    LOG('ZODB FS', PANIC, "%s ERROR: %s\n" % (packed_version,
+                                              (message % data)))
 
 def panic(message, *data):
-    message=message%data
-    LOG('ZODB FS',PANIC,"%s ERROR: %s\n" % (packed_version, message))
+    message = message % data
+    LOG('ZODB FS', PANIC, "%s ERROR: %s\n" % (packed_version, message))
     raise CorruptedTransactionError, message
 
 class FileStorageError(POSException.StorageError): pass
@@ -186,18 +195,16 @@ packed_version='FS21'
 
 class FileStorage(BaseStorage.BaseStorage,
                   ConflictResolution.ConflictResolvingStorage):
-    _packt=z64
+    # default pack time is 0
+    _packt = z64
 
     def __init__(self, file_name, create=0, read_only=0, stop=None,
                  quota=None):
 
-        if not os.path.exists(file_name):
-            create = 1
-
         if read_only:
             self._is_read_only = 1
             if create:
-                raise ValueError, "can\'t create a read-only file"
+                raise ValueError, "can't create a read-only file"
         elif stop is not None:
             raise ValueError, "time-travel is only supported in read-only mode"
 
@@ -230,14 +237,31 @@ class FileStorage(BaseStorage.BaseStorage,
         self._initIndex(index, vindex, tindex, tvindex)
         
         # Now open the file
-        
-        if create:
+
+        self._file = None
+        if not create:
+            try:
+                self._file = open(file_name, read_only and 'rb' or 'r+b')
+            except IOError, exc:
+                if exc.errno == errno.EFBIG:
+                    # The file is too big to open.  Fail visibly.
+                    raise
+                if exc.errno == errno.ENOENT:
+                    # The file doesn't exist.  Create it.
+                    create = 1
+                # If something else went wrong, it's hard to guess
+                # what the problem was.  If the file does not exist,
+                # create it.  Otherwise, fail.
+                if os.path.exists(file_name):
+                    raise
+                else:
+                    create = 1
+                    
+        if self._file is None and create:
             if os.path.exists(file_name):
                 os.remove(file_name)
             self._file = open(file_name, 'w+b')
             self._file.write(packed_version)
-        else:
-            self._file = open(file_name, read_only and 'rb' or 'r+b')
 
         r = self._restore_index()
         if r is not None:
@@ -1351,7 +1375,7 @@ class FileStorage(BaseStorage.BaseStorage,
             if self._packt != z64:
                 # Already packing.
                 raise FileStorageError, 'Already packing'
-            self._packt=stop
+            self._packt = stop
         finally:
             _lock_release()