| """File-like objects that read from or write to a string buffer. |
| |
| This implements (nearly) all stdio methods. |
| |
| f = StringIO() # ready for writing |
| f = StringIO(buf) # ready for reading |
| 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 |
| buf = f.readline() # read until end of line ('\n') or EOF |
| list = f.readlines()# list of f.readline() results until EOF |
| f.write(buf) # write at current position |
| f.writelines(list) # for line in list: f.write(line) |
| f.getvalue() # return whole file's contents as a string |
| |
| Notes: |
| - Using a real file is often faster (but less convenient). |
| - fileno() is left unimplemented so that code which uses it triggers |
| an exception early. |
| - Seeking far beyond EOF and then writing will insert real null |
| bytes that occupy space in the buffer. |
| - There's a simple test set (see end of this file). |
| """ |
| |
| import string |
| |
| class StringIO: |
| def __init__(self, buf = ''): |
| self.buf = buf |
| self.len = len(buf) |
| self.buflist = [] |
| self.pos = 0 |
| self.closed = 0 |
| self.softspace = 0 |
| def close(self): |
| if not self.closed: |
| self.closed = 1 |
| del self.buf, self.pos |
| 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 self.buflist: |
| self.buf = self.buf + string.joinfields(self.buflist, '') |
| self.buflist = [] |
| 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 self.buflist: |
| self.buf = self.buf + string.joinfields(self.buflist, '') |
| self.buflist = [] |
| if n < 0: |
| newpos = self.len |
| else: |
| newpos = min(self.pos+n, self.len) |
| r = self.buf[self.pos:newpos] |
| self.pos = newpos |
| return r |
| 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): |
| lines = [] |
| line = self.readline() |
| while line: |
| lines.append(line) |
| line = self.readline() |
| return lines |
| 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) |
| if self.pos < self.len: |
| if self.buflist: |
| self.buf = self.buf + string.joinfields(self.buflist, '') |
| self.buflist = [] |
| self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]] |
| self.buf = '' |
| else: |
| self.buflist.append(s) |
| self.len = newpos |
| 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" |
| def getvalue(self): |
| if self.buflist: |
| self.buf = self.buf + string.joinfields(self.buflist, '') |
| self.buflist = [] |
| return self.buf |
| |
| |
| # 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 =', `f.readline()` |
| here = f.tell() |
| line = f.readline() |
| print 'Second line =', `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() |