1# class MkMemoIO implements file-like objects that read/write a 2# memo field in a Metakit database (either on file, or in memory). 3# 4# A simple adaptation of the StringIO.py module, by Jean-Claude Wippler. 5# 6# This implements (nearly) all stdio methods. 7# 8# f = MkMemoIO(view, memoprop, rownum) # setup for view[rownum].memoprop 9# f.close() # explicitly release resources held 10# flag = f.isatty() # always false 11# pos = f.tell() # get current position 12# f.seek(pos) # set current position 13# f.seek(pos, mode) # mode 0: absolute; 1: relative; 2: relative to EOF 14# buf = f.read() # read until EOF 15# buf = f.read(n) # read up to n bytes 16# buf = f.readline() # read until end of line ('\n') or EOF 17# list = f.readlines()# list of f.readline() results until EOF 18# f.write(buf) # write at current position 19# f.writelines(list) # for line in list: f.write(line) 20# f.getvalue() # return whole file's contents as a string 21# 22# Notes: 23# - fileno() is left unimplemented so that code which uses it triggers 24# an exception early. 25# - Seeking beyond EOF and then writing will insert garbage, unlike the 26# StringIO class which clears, and from which this code was adapted. 27# - There's a simple test set (see end of this file). 28# - write() has an optional "resize" to insert (>0) or delete (<0) bytes. 29# To merely insert/delete, write an empty string. The resize value is 30# adjusted to a "reasonable" range. Inserted bytes are *not* cleared. 31 32import string, sys 33 34class MkMemoIO: 35 def __init__(self, view, memo, row): 36 self.view = view 37 self.memo = memo 38 self.row = row 39 self.pos = 0 40 self.closed = 0 41 self.softspace = 0 42 def close(self): 43 if not self.closed: 44 self.closed = 1 45 del self.view, self.memo, self.row, self.pos 46 def isatty(self): 47 if self.closed: 48 raise ValueError, "I/O operation on closed file" 49 return 0 50 def seek(self, pos, mode = 0): 51 if self.closed: 52 raise ValueError, "I/O operation on closed file" 53 if mode == 1: 54 pos = pos + self.pos 55 elif mode == 2: 56 pos = pos + self.view.itemsize(self.memo, self.row) 57 self.pos = max(0, pos) 58 def tell(self): 59 if self.closed: 60 raise ValueError, "I/O operation on closed file" 61 return self.pos 62 def read(self, n = -1): 63 if self.closed: 64 raise ValueError, "I/O operation on closed file" 65 if n == 0: 66 return "" 67 r = self.view.access(self.memo, self.row, self.pos, n) 68 self.pos = self.pos + len(r) 69 return r 70 def readline(self, length=None): 71 if self.closed: 72 raise ValueError, "I/O operation on closed file" 73 remain = self.view.itemsize(self.memo, self.row) - self.pos 74 if length is None: 75 length = remain 76 length = min(length, remain) 77 i = -1 78 oldpos = self.pos 79 for o in xrange(0, length, 100): 80 i = string.find(self.read(100), '\n') 81 if i >= 0: 82 break 83 self.pos = oldpos 84 if i >= 0: 85 length = o+i+1 86 return self.read(length) 87 def readlines(self): 88 lines = [] 89 line = self.readline() 90 while line: 91 lines.append(line) 92 line = self.readline() 93 return lines 94 def write(self, s, resize=0): 95 if self.closed: 96 raise ValueError, "I/O operation on closed file" 97 self.view.modify(self.memo, self.row, s, self.pos, resize) 98 self.pos = self.pos + len(s) 99 def writelines(self, list): 100 for line in list: self.write(line) 101 def flush(self): 102 if self.closed: 103 raise ValueError, "I/O operation on closed file" 104 def getvalue(self): 105 return self.view.access(self.memo, self.row, 0) 106 107 108# A little test suite 109 110def test(): 111 import Mk4py 112 mk=Mk4py 113 db=mk.storage() 114 vw=db.getas('v[m:M]') 115 vw.append() 116 if sys.argv[1:]: 117 file = sys.argv[1] 118 else: 119 file = '/etc/passwd' 120 lines = open(file, 'r').readlines() 121 text = open(file, 'r').read() 122 f = MkMemoIO(vw,vw.m,0) 123 for line in lines[:-2]: 124 f.write(line) 125 f.writelines(lines[-2:]) 126 if f.getvalue() != text: 127 raise RuntimeError, 'write failed' 128 length = f.tell() 129 print 'File length =', length 130 f.seek(len(lines[0])) 131 f.write(lines[1]) 132 f.seek(0) 133 print 'First line =', `f.readline()` 134 here = f.tell() 135 line = f.readline() 136 print 'Second line =', `line` 137 f.seek(-len(line), 1) 138 line2 = f.read(len(line)) 139 if line != line2: 140 raise RuntimeError, 'bad result after seek back' 141 f.seek(len(line2), 1) 142 list = f.readlines() 143 line = list[-1] 144 f.seek(f.tell() - len(line)) 145 line2 = f.read() 146 if line != line2: 147 raise RuntimeError, 'bad result after seek back from EOF' 148 print 'Read', len(list), 'more lines' 149 print 'File length =', f.tell() 150 if f.tell() != length: 151 raise RuntimeError, 'bad length' 152 f.close() 153 154if __name__ == '__main__': 155 test() 156