cpython/Lib/ArrayIO.py

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