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3645
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1 """File-like objects that read/write an array buffer.
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2
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3 This implements (nearly) all stdio methods.
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4
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5 f = ArrayIO() # ready for writing
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6 f = ArrayIO(buf) # ready for reading
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7 f.close() # explicitly release resources held
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8 flag = f.isatty() # always false
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9 pos = f.tell() # get current position
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10 f.seek(pos) # set current position
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11 f.seek(pos, mode) # mode 0: absolute; 1: relative; 2: relative to EOF
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12 buf = f.read() # read until EOF
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13 buf = f.read(n) # read up to n bytes
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14 buf = f.readline() # read until end of line ('\n') or EOF
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15 list = f.readlines()# list of f.readline() results until EOF
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16 f.write(buf) # write at current position
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17 f.writelines(list) # for line in list: f.write(line)
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18 f.getvalue() # return whole file's contents as a string
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19
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20 Notes:
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21 - This is very similar to StringIO. StringIO is faster for reading,
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22 but ArrayIO is faster for writing.
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23 - ArrayIO uses an array object internally, but all its interfaces
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24 accept and return strings.
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25 - Using a real file is often faster (but less convenient).
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26 - fileno() is left unimplemented so that code which uses it triggers
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27 an exception early.
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28 - Seeking far beyond EOF and then writing will insert real null
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29 bytes that occupy space in the buffer.
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30 - There's a simple test set (see end of this file).
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31 """
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3423
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32
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33 import string
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3645
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34 from array import array
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3423
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35
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3645
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36 class ArrayIO:
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3423
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37 def __init__(self, buf = ''):
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3645
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38 self.buf = array('c', buf)
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39 self.pos = 0
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40 self.closed = 0
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41 self.softspace = 0
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42 def close(self):
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43 if not self.closed:
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44 self.closed = 1
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45 del self.buf, self.pos
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46 def isatty(self):
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47 return 0
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48 def seek(self, pos, mode = 0):
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49 if mode == 1:
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50 pos = pos + self.pos
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51 elif mode == 2:
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52 pos = pos + len(self.buf)
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53 self.pos = max(0, pos)
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54 def tell(self):
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55 return self.pos
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56 def read(self, n = -1):
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57 if n < 0:
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58 newpos = len(self.buf)
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59 else:
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60 newpos = min(self.pos+n, len(self.buf))
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61 r = self.buf[self.pos:newpos].tostring()
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62 self.pos = newpos
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63 return r
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64 def readline(self):
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3645
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65 i = string.find(self.buf[self.pos:].tostring(), '\n')
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66 if i < 0:
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67 newpos = len(self.buf)
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68 else:
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3645
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69 newpos = self.pos+i+1
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70 r = self.buf[self.pos:newpos].tostring()
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71 self.pos = newpos
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72 return r
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3645
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73 def readlines(self):
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74 lines = string.splitfields(self.read(), '\n')
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75 if not lines:
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76 return lines
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77 for i in range(len(lines)-1):
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78 lines[i] = lines[i] + '\n'
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79 if not lines[-1]:
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80 del lines[-1]
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81 return lines
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82 def write(self, s):
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83 if not s: return
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3645
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84 a = array('c', s)
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85 n = self.pos - len(self.buf)
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86 if n > 0:
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87 self.buf[len(self.buf):] = array('c', '\0')*n
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88 newpos = self.pos + len(a)
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89 self.buf[self.pos:newpos] = a
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90 self.pos = newpos
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91 def writelines(self, list):
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92 self.write(string.joinfields(list, ''))
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93 def flush(self):
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94 pass
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95 def getvalue(self):
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96 return self.buf.tostring()
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97
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98
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99 # A little test suite
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100
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101 def test():
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102 import sys
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103 if sys.argv[1:]:
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104 file = sys.argv[1]
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105 else:
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106 file = '/etc/passwd'
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107 lines = open(file, 'r').readlines()
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108 text = open(file, 'r').read()
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109 f = ArrayIO()
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110 for line in lines[:-2]:
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111 f.write(line)
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112 f.writelines(lines[-2:])
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113 if f.getvalue() != text:
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114 raise RuntimeError, 'write failed'
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115 length = f.tell()
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116 print 'File length =', length
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117 f.seek(len(lines[0]))
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118 f.write(lines[1])
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119 f.seek(0)
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120 print 'First line =', `f.readline()`
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121 here = f.tell()
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122 line = f.readline()
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123 print 'Second line =', `line`
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124 f.seek(-len(line), 1)
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125 line2 = f.read(len(line))
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126 if line != line2:
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127 raise RuntimeError, 'bad result after seek back'
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128 f.seek(len(line2), 1)
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129 list = f.readlines()
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130 line = list[-1]
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131 f.seek(f.tell() - len(line))
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132 line2 = f.read()
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133 if line != line2:
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134 raise RuntimeError, 'bad result after seek back from EOF'
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135 print 'Read', len(list), 'more lines'
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136 print 'File length =', f.tell()
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137 if f.tell() != length:
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138 raise RuntimeError, 'bad length'
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139 f.close()
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140
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141 if __name__ == '__main__':
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142 test()
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