"""File-like objects that read from or write to a bsddb record. This implements (nearly) all stdio methods. f = DBRecIO(db, key, txn=None)f.close()           # explicitly release resources heldflag = f.isatty()   # always falsepos = f.tell()      # get current positionf.seek(pos)         # set current positionf.seek(pos, mode)   # mode 0: absolute; 1: relative; 2: relative to EOFbuf = f.read()      # read until EOFbuf = f.read(n)     # read up to n bytesf.truncate([size])  # truncate file at to at most size (default: current pos)f.write(buf)        # write at current positionf.writelines(list)  # for line in list: f.write(line) Notes:- fileno() is left unimplemented so that code which uses it triggers  an exception early.- There's a simple test set (see end of this file) - not yet updated  for DBRecIO.- readline() is not implemented yet.  From:    Itamar Shtull-Trauring <itamar@maxnm.com>""" import errnoimport string class DBRecIO:    def __init__(self, db, key, txn=None):        self.db = db        self.key = key        self.txn = txn        self.len = None        self.pos = 0        self.closed = 0        self.softspace = 0     def close(self):        if not self.closed:            self.closed = 1            del self.db, self.txn     def isatty(self):        if self.closed:            raise ValueError, "I/O operation on closed file"        return 0     def seek(self, pos, mode = 0):        if self.closed:            raise ValueError, "I/O operation on closed file"        if mode == 1:            pos = pos + self.pos        elif mode == 2:            pos = pos + self.len        self.pos = max(0, pos)     def tell(self):        if self.closed:            raise ValueError, "I/O operation on closed file"        return self.pos     def read(self, n = -1):        if self.closed:            raise ValueError, "I/O operation on closed file"        if n < 0:            newpos = self.len        else:            newpos = min(self.pos+n, self.len)         dlen = newpos - self.pos         r = self.db.get(self.key, txn=self.txn, dlen=dlen, doff=self.pos)        self.pos = newpos        return r     __fixme = """    def readline(self, length=None):        if self.closed:            raise ValueError, "I/O operation on closed file"        if self.buflist:            self.buf = self.buf + string.joinfields(self.buflist, '')            self.buflist = []        i = string.find(self.buf, '\n', self.pos)        if i < 0:            newpos = self.len        else:            newpos = i+1        if length is not None:            if self.pos + length < newpos:                newpos = self.pos + length        r = self.buf[self.pos:newpos]        self.pos = newpos        return r     def readlines(self, sizehint = 0):        total = 0        lines = []        line = self.readline()        while line:            lines.append(line)            total += len(line)            if 0 < sizehint <= total:                break            line = self.readline()        return lines    """     def truncate(self, size=None):        if self.closed:            raise ValueError, "I/O operation on closed file"        if size is None:            size = self.pos        elif size < 0:            raise IOError(errno.EINVAL,                                      "Negative size not allowed")        elif size < self.pos:            self.pos = size        self.db.put(self.key, "", txn=self.txn, dlen=self.len-size, doff=size)     def write(self, s):        if self.closed:            raise ValueError, "I/O operation on closed file"        if not s: return        if self.pos > self.len:            self.buflist.append('\0'*(self.pos - self.len))            self.len = self.pos        newpos = self.pos + len(s)        self.db.put(self.key, s, txn=self.txn, dlen=len(s), doff=self.pos)        self.pos = newpos     def writelines(self, list):        self.write(string.joinfields(list, ''))     def flush(self):        if self.closed:            raise ValueError, "I/O operation on closed file"  """# A little test suite def _test():    import sys    if sys.argv[1:]:        file = sys.argv[1]    else:        file = '/etc/passwd'    lines = open(file, 'r').readlines()    text = open(file, 'r').read()    f = StringIO()    for line in lines[:-2]:        f.write(line)    f.writelines(lines[-2:])    if f.getvalue() != text:        raise RuntimeError, 'write failed'    length = f.tell()    print 'File length =', length    f.seek(len(lines[0]))    f.write(lines[1])    f.seek(0)    print 'First line =', repr(f.readline())    here = f.tell()    line = f.readline()    print 'Second line =', repr(line)    f.seek(-len(line), 1)    line2 = f.read(len(line))    if line != line2:        raise RuntimeError, 'bad result after seek back'    f.seek(len(line2), 1)    list = f.readlines()    line = list[-1]    f.seek(f.tell() - len(line))    line2 = f.read()    if line != line2:        raise RuntimeError, 'bad result after seek back from EOF'    print 'Read', len(list), 'more lines'    print 'File length =', f.tell()    if f.tell() != length:        raise RuntimeError, 'bad length'    f.close() if __name__ == '__main__':    _test()"""