portalocker.py 文件源码

def __init__(self, filename, mode='rb'):
        self.filename = filename
        self.mode = mode
        self.file = None
        if 'r' in mode:
            self.file = open_file(filename, mode)
            lock(self.file, LOCK_SH)
        elif 'w' in mode or 'a' in mode:
            self.file = open_file(filename, mode.replace('w', 'a'))
            lock(self.file, LOCK_EX)
            if 'a' not in mode:
                self.file.seek(0)
                self.file.truncate(0)
        else:
            raise RuntimeError("invalid LockedFile(...,mode)")