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142 lines
3.7 KiB
Python
Executable file
142 lines
3.7 KiB
Python
Executable file
"""File-like objects that read/write an array buffer.
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This implements (nearly) all stdio methods.
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f = ArrayIO() # ready for writing
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f = ArrayIO(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.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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- This is very similar to StringIO. StringIO is faster for reading,
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but ArrayIO is faster for writing.
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- ArrayIO uses an array object internally, but all its interfaces
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accept and return strings.
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- Using a real file is often faster (but less convenient).
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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 string
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from array import array
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class ArrayIO:
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def __init__(self, buf = ''):
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self.buf = array('c', buf)
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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 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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return 0
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def seek(self, pos, mode = 0):
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if mode == 1:
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pos = pos + self.pos
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elif mode == 2:
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pos = pos + len(self.buf)
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self.pos = max(0, pos)
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def tell(self):
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return self.pos
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def read(self, n = -1):
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if n < 0:
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newpos = len(self.buf)
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else:
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newpos = min(self.pos+n, len(self.buf))
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r = self.buf[self.pos:newpos].tostring()
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self.pos = newpos
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return r
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def readline(self):
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i = string.find(self.buf[self.pos:].tostring(), '\n')
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if i < 0:
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newpos = len(self.buf)
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else:
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newpos = self.pos+i+1
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r = self.buf[self.pos:newpos].tostring()
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self.pos = newpos
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return r
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def readlines(self):
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lines = string.splitfields(self.read(), '\n')
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if not lines:
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return lines
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for i in range(len(lines)-1):
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lines[i] = lines[i] + '\n'
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if not lines[-1]:
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del lines[-1]
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return lines
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def write(self, s):
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if not s: return
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a = array('c', s)
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n = self.pos - len(self.buf)
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if n > 0:
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self.buf[len(self.buf):] = array('c', '\0')*n
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newpos = self.pos + len(a)
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self.buf[self.pos:newpos] = a
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self.pos = newpos
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def writelines(self, list):
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self.write(string.joinfields(list, ''))
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def flush(self):
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pass
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def getvalue(self):
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return self.buf.tostring()
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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 = ArrayIO()
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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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here = 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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