Edit File: dbrecio.py
""" 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 held flag = f.isatty() # always false pos = f.tell() # get current position f.seek(pos) # set current position f.seek(pos, mode) # mode 0: absolute; 1: relative; 2: relative to EOF buf = f.read() # read until EOF buf = f.read(n) # read up to n bytes f.truncate([size]) # truncate file at to at most size (default: current pos) f.write(buf) # write at current position f.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 errno import 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() """
Back to File Manager