218 lines
6.3 KiB
Python
218 lines
6.3 KiB
Python
"""File-like objects that read from or write to a string buffer.
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This implements (nearly) all stdio methods.
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f = StringIO() # ready for writing
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f = StringIO(buf) # ready for reading
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f.close() # explicitly release resources held
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flag = f.isatty() # always false
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pos = f.tell() # get current position
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f.seek(pos) # set current position
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f.seek(pos, mode) # mode 0: absolute; 1: relative; 2: relative to EOF
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buf = f.read() # read until EOF
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buf = f.read(n) # read up to n bytes
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buf = f.readline() # read until end of line ('\n') or EOF
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list = f.readlines()# list of f.readline() results until EOF
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f.truncate([size]) # truncate file at to at most size (default: current pos)
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f.write(buf) # write at current position
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f.writelines(list) # for line in list: f.write(line)
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f.getvalue() # return whole file's contents as a string
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Notes:
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- Using a real file is often faster (but less convenient).
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- There's also a much faster implementation in C, called cStringIO, but
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it's not subclassable.
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- fileno() is left unimplemented so that code which uses it triggers
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an exception early.
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- Seeking far beyond EOF and then writing will insert real null
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bytes that occupy space in the buffer.
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- There's a simple test set (see end of this file).
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"""
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import types
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try:
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from errno import EINVAL
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except ImportError:
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EINVAL = 22
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__all__ = ["StringIO"]
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class StringIO:
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def __init__(self, buf = ''):
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# Force self.buf to be a string or unicode
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if type(buf) is not types.UnicodeType:
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buf = str(buf)
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self.buf = buf
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self.len = len(buf)
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self.buflist = []
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self.pos = 0
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self.closed = 0
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self.softspace = 0
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def __iter__(self):
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return iter(self.readline, '')
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def close(self):
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if not self.closed:
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self.closed = 1
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del self.buf, self.pos
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def isatty(self):
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if self.closed:
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raise ValueError, "I/O operation on closed file"
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return 0
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def seek(self, pos, mode = 0):
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if self.closed:
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raise ValueError, "I/O operation on closed file"
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if self.buflist:
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self.buf += ''.join(self.buflist)
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self.buflist = []
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if mode == 1:
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pos += self.pos
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elif mode == 2:
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pos += self.len
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self.pos = max(0, pos)
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def tell(self):
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if self.closed:
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raise ValueError, "I/O operation on closed file"
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return self.pos
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def read(self, n = -1):
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if self.closed:
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raise ValueError, "I/O operation on closed file"
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if self.buflist:
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self.buf += ''.join(self.buflist)
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self.buflist = []
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if n < 0:
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newpos = self.len
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else:
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newpos = min(self.pos+n, self.len)
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r = self.buf[self.pos:newpos]
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self.pos = newpos
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return r
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def readline(self, length=None):
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if self.closed:
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raise ValueError, "I/O operation on closed file"
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if self.buflist:
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self.buf += ''.join(self.buflist)
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self.buflist = []
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i = self.buf.find('\n', self.pos)
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if i < 0:
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newpos = self.len
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else:
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newpos = i+1
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if length is not None:
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if self.pos + length < newpos:
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newpos = self.pos + length
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r = self.buf[self.pos:newpos]
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self.pos = newpos
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return r
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def readlines(self, sizehint = 0):
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total = 0
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lines = []
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line = self.readline()
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while line:
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lines.append(line)
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total += len(line)
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if 0 < sizehint <= total:
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break
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line = self.readline()
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return lines
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def truncate(self, size=None):
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if self.closed:
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raise ValueError, "I/O operation on closed file"
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if size is None:
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size = self.pos
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elif size < 0:
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raise IOError(EINVAL, "Negative size not allowed")
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elif size < self.pos:
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self.pos = size
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self.buf = self.getvalue()[:size]
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def write(self, s):
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if self.closed:
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raise ValueError, "I/O operation on closed file"
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if not s: return
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# Force s to be a string or unicode
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if type(s) is not types.UnicodeType:
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s = str(s)
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if self.pos > self.len:
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self.buflist.append('\0'*(self.pos - self.len))
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self.len = self.pos
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newpos = self.pos + len(s)
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if self.pos < self.len:
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if self.buflist:
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self.buf += ''.join(self.buflist)
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self.buflist = []
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self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]]
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self.buf = ''
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if newpos > self.len:
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self.len = newpos
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else:
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self.buflist.append(s)
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self.len = newpos
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self.pos = newpos
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def writelines(self, list):
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self.write(''.join(list))
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def flush(self):
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if self.closed:
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raise ValueError, "I/O operation on closed file"
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def getvalue(self):
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if self.buflist:
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self.buf += ''.join(self.buflist)
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self.buflist = []
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return self.buf
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# A little test suite
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def test():
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import sys
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if sys.argv[1:]:
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file = sys.argv[1]
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else:
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file = '/etc/passwd'
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lines = open(file, 'r').readlines()
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text = open(file, 'r').read()
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f = StringIO()
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for line in lines[:-2]:
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f.write(line)
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f.writelines(lines[-2:])
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if f.getvalue() != text:
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raise RuntimeError, 'write failed'
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length = f.tell()
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print 'File length =', length
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f.seek(len(lines[0]))
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f.write(lines[1])
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f.seek(0)
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print 'First line =', `f.readline()`
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print 'Position =', f.tell()
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line = f.readline()
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print 'Second line =', `line`
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f.seek(-len(line), 1)
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line2 = f.read(len(line))
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if line != line2:
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raise RuntimeError, 'bad result after seek back'
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f.seek(len(line2), 1)
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list = f.readlines()
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line = list[-1]
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f.seek(f.tell() - len(line))
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line2 = f.read()
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if line != line2:
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raise RuntimeError, 'bad result after seek back from EOF'
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print 'Read', len(list), 'more lines'
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print 'File length =', f.tell()
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if f.tell() != length:
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raise RuntimeError, 'bad length'
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f.close()
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if __name__ == '__main__':
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test()
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