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/Lib/bsddb/dbrecio.py

http://unladen-swallow.googlecode.com/
Python | 190 lines | 145 code | 3 blank | 42 comment | 4 complexity | 72bbb3286311ff35b619f6646267c3b5 MD5 | raw file
  1
  2"""
  3File-like objects that read from or write to a bsddb record.
  4
  5This implements (nearly) all stdio methods.
  6
  7f = DBRecIO(db, key, txn=None)
  8f.close()           # explicitly release resources held
  9flag = f.isatty()   # always false
 10pos = f.tell()      # get current position
 11f.seek(pos)         # set current position
 12f.seek(pos, mode)   # mode 0: absolute; 1: relative; 2: relative to EOF
 13buf = f.read()      # read until EOF
 14buf = f.read(n)     # read up to n bytes
 15f.truncate([size])  # truncate file at to at most size (default: current pos)
 16f.write(buf)        # write at current position
 17f.writelines(list)  # for line in list: f.write(line)
 18
 19Notes:
 20- fileno() is left unimplemented so that code which uses it triggers
 21  an exception early.
 22- There's a simple test set (see end of this file) - not yet updated
 23  for DBRecIO.
 24- readline() is not implemented yet.
 25
 26
 27From:
 28    Itamar Shtull-Trauring <itamar@maxnm.com>
 29"""
 30
 31import errno
 32import string
 33
 34class DBRecIO:
 35    def __init__(self, db, key, txn=None):
 36        self.db = db
 37        self.key = key
 38        self.txn = txn
 39        self.len = None
 40        self.pos = 0
 41        self.closed = 0
 42        self.softspace = 0
 43
 44    def close(self):
 45        if not self.closed:
 46            self.closed = 1
 47            del self.db, self.txn
 48
 49    def isatty(self):
 50        if self.closed:
 51            raise ValueError, "I/O operation on closed file"
 52        return 0
 53
 54    def seek(self, pos, mode = 0):
 55        if self.closed:
 56            raise ValueError, "I/O operation on closed file"
 57        if mode == 1:
 58            pos = pos + self.pos
 59        elif mode == 2:
 60            pos = pos + self.len
 61        self.pos = max(0, pos)
 62
 63    def tell(self):
 64        if self.closed:
 65            raise ValueError, "I/O operation on closed file"
 66        return self.pos
 67
 68    def read(self, n = -1):
 69        if self.closed:
 70            raise ValueError, "I/O operation on closed file"
 71        if n < 0:
 72            newpos = self.len
 73        else:
 74            newpos = min(self.pos+n, self.len)
 75
 76        dlen = newpos - self.pos
 77
 78        r = self.db.get(self.key, txn=self.txn, dlen=dlen, doff=self.pos)
 79        self.pos = newpos
 80        return r
 81
 82    __fixme = """
 83    def readline(self, length=None):
 84        if self.closed:
 85            raise ValueError, "I/O operation on closed file"
 86        if self.buflist:
 87            self.buf = self.buf + string.joinfields(self.buflist, '')
 88            self.buflist = []
 89        i = string.find(self.buf, '\n', self.pos)
 90        if i < 0:
 91            newpos = self.len
 92        else:
 93            newpos = i+1
 94        if length is not None:
 95            if self.pos + length < newpos:
 96                newpos = self.pos + length
 97        r = self.buf[self.pos:newpos]
 98        self.pos = newpos
 99        return r
100
101    def readlines(self, sizehint = 0):
102        total = 0
103        lines = []
104        line = self.readline()
105        while line:
106            lines.append(line)
107            total += len(line)
108            if 0 < sizehint <= total:
109                break
110            line = self.readline()
111        return lines
112    """
113
114    def truncate(self, size=None):
115        if self.closed:
116            raise ValueError, "I/O operation on closed file"
117        if size is None:
118            size = self.pos
119        elif size < 0:
120            raise IOError(errno.EINVAL,
121                                      "Negative size not allowed")
122        elif size < self.pos:
123            self.pos = size
124        self.db.put(self.key, "", txn=self.txn, dlen=self.len-size, doff=size)
125
126    def write(self, s):
127        if self.closed:
128            raise ValueError, "I/O operation on closed file"
129        if not s: return
130        if self.pos > self.len:
131            self.buflist.append('\0'*(self.pos - self.len))
132            self.len = self.pos
133        newpos = self.pos + len(s)
134        self.db.put(self.key, s, txn=self.txn, dlen=len(s), doff=self.pos)
135        self.pos = newpos
136
137    def writelines(self, list):
138        self.write(string.joinfields(list, ''))
139
140    def flush(self):
141        if self.closed:
142            raise ValueError, "I/O operation on closed file"
143
144
145"""
146# A little test suite
147
148def _test():
149    import sys
150    if sys.argv[1:]:
151        file = sys.argv[1]
152    else:
153        file = '/etc/passwd'
154    lines = open(file, 'r').readlines()
155    text = open(file, 'r').read()
156    f = StringIO()
157    for line in lines[:-2]:
158        f.write(line)
159    f.writelines(lines[-2:])
160    if f.getvalue() != text:
161        raise RuntimeError, 'write failed'
162    length = f.tell()
163    print 'File length =', length
164    f.seek(len(lines[0]))
165    f.write(lines[1])
166    f.seek(0)
167    print 'First line =', repr(f.readline())
168    here = f.tell()
169    line = f.readline()
170    print 'Second line =', repr(line)
171    f.seek(-len(line), 1)
172    line2 = f.read(len(line))
173    if line != line2:
174        raise RuntimeError, 'bad result after seek back'
175    f.seek(len(line2), 1)
176    list = f.readlines()
177    line = list[-1]
178    f.seek(f.tell() - len(line))
179    line2 = f.read()
180    if line != line2:
181        raise RuntimeError, 'bad result after seek back from EOF'
182    print 'Read', len(list), 'more lines'
183    print 'File length =', f.tell()
184    if f.tell() != length:
185        raise RuntimeError, 'bad length'
186    f.close()
187
188if __name__ == '__main__':
189    _test()
190"""