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"""
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
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
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 + ''.join(self.buflist)
self.buflist = []
i = self.buf.find('\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(''.join(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()
"""
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