Hi everybody:
I played with the class Flock and changed the line win32con.FILE_SHARE_READ|win32con.FILE_SHARE_WRITE,\ to win32con.FILE_SHARE_READ,\ and now I cannot copy the file over which suits me.
When file is NOT locked I get:
E:\>copy d:\log.txt .
Overwrite .\log.txt? (Yes/No/All): y
1 file(s) copied.When file IS locked I get:
E:\>copy d:\log.txt .
The process cannot access the file because it is being used by another process.
0 file(s) copied.
Below is the new script completely. Note that when upgrading to Python v2.4 I had to change self.highbits from 0xffff0000 to -0x7fff0000.
-----SCRIPT STARTS----
import win32file import win32con import win32security import pywintypes
class Flock:
def __init__(self,file):
self.file=file
secur_att = win32security.SECURITY_ATTRIBUTES()
secur_att.Initialize()
self.highbits=-0x7fff0000
self.hfile=win32file.CreateFile( self.file,\
win32con.GENERIC_READ|win32con.GENERIC_WRITE,\
win32con.FILE_SHARE_READ,\
secur_att,\
win32con.OPEN_ALWAYS,\
win32con.FILE_ATTRIBUTE_NORMAL , 0) def lock(self):
lock_flags=win32con.LOCKFILE_EXCLUSIVE_LOCK|\
win32con.LOCKFILE_FAIL_IMMEDIATELY
self.ov=pywintypes.OVERLAPPED()
win32file.LockFileEx(self.hfile,lock_flags,0,\
self.highbits,self.ov) def unlock(self):
win32file.UnlockFileEx(self.hfile,0,\
self.highbits,self.ov)
self.hfile.Close()if __name__ == '__main__':
import sys
l=Flock("e:\\\\log.txt")
print 'calling lock'
l.lock()
print "Now locked. Hit enter to release lock."
dummy = sys.stdin.readline() l.unlock()
print 'now unlocked'-----SCRIPT ENDS----
-pekka-
Pekka Niiranen wrote:
Hi,
I have used the following example from win32 extensions:
-----SCRIPT STARTS----
import win32file import win32con import win32security import pywintypes
class Flock: def __init__(self,file): self.file=file secur_att = win32security.SECURITY_ATTRIBUTES() secur_att.Initialize() self.highbits=-0x7fff0000 self.hfile=win32file.CreateFile( self.file,\ win32con.GENERIC_READ|win32con.GENERIC_WRITE,\ win32con.FILE_SHARE_READ|win32con.FILE_SHARE_WRITE,\ secur_att, win32con.OPEN_ALWAYS,\ win32con.FILE_ATTRIBUTE_NORMAL , 0 ) def lock(self): lock_flags=win32con.LOCKFILE_EXCLUSIVE_LOCK|\ win32con.LOCKFILE_FAIL_IMMEDIATELY self.ov=pywintypes.OVERLAPPED() win32file.LockFileEx(self.hfile,lock_flags,0,\ self.highbits,self.ov) def unlock(self): win32file.UnlockFileEx(self.hfile,0,\ self.highbits,self.ov) self.hfile.Close()
if __name__ == '__main__':
from time import time, strftime, localtime
import sys
l=Flock("e:\\\\log.txt")
print 'calling lock'
l.lock()
print "Now locked. Hit enter to release lock."
dummy = sys.stdin.readline()
l.unlock() print 'now unlocked'
-----SCRIPT ENDS----
If I start one python process from dos window I get message:
E:\>python lockker.py calling lock Now locked. Hit enter to release lock.
All well, now if
1) I start another Dos -shell and run the same command I get:
E:\>python lockker.py calling lock Traceback (most recent call last): File "lockker.py", line 35, in ? l.lock() File "lockker.py", line 23, in lock win32file.LockFileEx(self.hfile,lock_flags,0,\ self.highbits,self.ov) pywintypes.error: (33, 'LockFileEx',\ 'The process cannot access the file because\ another process has locked a portion of the file.')
Which is correct.
2) I try to read the contents of the file from Dos -shell, I get:
E:\>type log.txt
The process cannot access the file because another\
process has locked a portion of the file.
This is correct.
3) When I open the file into notepad.exe I can edit the screen but not write changes to disk. Correct again!
4) I cannot delete the file from Dos shell or from W2K explorer which is correct.
5) However, I can overwrite the file over with: E:\>copy d:\log.txt log.txt 1 file(s) copied.
Which is WRONG as is me being able to copy another file over it with W2K explorer too.
Is there a way around this? How can I stop file being COPIED OVER while it is being open? Is this window's feature? Is readlines() operation "atomic" enough for me not to worry about these issues?
My python script modifies set of files from a directory one by one. I try to lock them all exclusively for the script until all are modified. If one of the files gets overwritten by another version (by another process) the script may fail.
-pekka-
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