Mercurial > cpython-lru_cache-weakref

annotate Lib/StringIO.py @ 20354:fdc1914406e2 legacy-trunk

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Updated, and added a very terse description of PyMac_SetConsoleHandler().
author Jack Jansen <jack.jansen@cwi.nl>
date Tue, 09 Oct 2001 23:14:06 +0000
parents ccec02bfe9a0
children 6b0e16cb65d5
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1 """File-like objects that read from or write to a string 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 = StringIO() # ready for writing
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6 f = StringIO(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.truncate([size]) # truncate file at to at most size (default: current pos)
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17 f.write(buf) # write at current position
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18 f.writelines(list) # for line in list: f.write(line)
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19 f.getvalue() # return whole file's contents as a string
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20
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21 Notes:
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22 - Using a real file is often faster (but less convenient).
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23 - There's also a much faster implementation in C, called cStringIO, but
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24 it's not subclassable.
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25 - fileno() is left unimplemented so that code which uses it triggers
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26 an exception early.
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27 - Seeking far beyond EOF and then writing will insert real null
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28 bytes that occupy space in the buffer.
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29 - There's a simple test set (see end of this file).
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30 """
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31
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32 try:
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33 from errno import EINVAL
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34 except ImportError:
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35 EINVAL = 22
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36
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37 __all__ = ["StringIO"]
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38
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39 class StringIO:
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40 def __init__(self, buf = ''):
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41 # Force self.buf to be a string
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42 self.buf = str(buf)
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43 self.len = len(buf)
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44 self.buflist = []
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45 self.pos = 0
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46 self.closed = 0
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47 self.softspace = 0
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48
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49 def __iter__(self):
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50 return iter(self.readline, '')
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51
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52 def close(self):
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53 if not self.closed:
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54 self.closed = 1
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55 del self.buf, self.pos
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56
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57 def isatty(self):
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58 if self.closed:
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59 raise ValueError, "I/O operation on closed file"
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60 return 0
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61
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62 def seek(self, pos, mode = 0):
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63 if self.closed:
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64 raise ValueError, "I/O operation on closed file"
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65 if self.buflist:
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66 self.buf += ''.join(self.buflist)
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67 self.buflist = []
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68 if mode == 1:
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69 pos += self.pos
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70 elif mode == 2:
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71 pos += self.len
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72 self.pos = max(0, pos)
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73
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74 def tell(self):
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75 if self.closed:
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76 raise ValueError, "I/O operation on closed file"
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77 return self.pos
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78
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79 def read(self, n = -1):
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80 if self.closed:
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81 raise ValueError, "I/O operation on closed file"
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82 if self.buflist:
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83 self.buf += ''.join(self.buflist)
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84 self.buflist = []
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85 if n < 0:
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86 newpos = self.len
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87 else:
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88 newpos = min(self.pos+n, self.len)
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89 r = self.buf[self.pos:newpos]
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90 self.pos = newpos
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91 return r
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92
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93 def readline(self, length=None):
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94 if self.closed:
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95 raise ValueError, "I/O operation on closed file"
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96 if self.buflist:
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97 self.buf += ''.join(self.buflist)
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98 self.buflist = []
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99 i = self.buf.find('\n', self.pos)
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100 if i < 0:
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101 newpos = self.len
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102 else:
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103 newpos = i+1
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104 if length is not None:
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105 if self.pos + length < newpos:
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106 newpos = self.pos + length
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107 r = self.buf[self.pos:newpos]
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108 self.pos = newpos
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109 return r
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110
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111 def readlines(self, sizehint = 0):
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112 total = 0
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113 lines = []
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114 line = self.readline()
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115 while line:
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116 lines.append(line)
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117 total += len(line)
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118 if 0 < sizehint <= total:
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119 break
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120 line = self.readline()
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121 return lines
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122
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123 def truncate(self, size=None):
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124 if self.closed:
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125 raise ValueError, "I/O operation on closed file"
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126 if size is None:
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127 size = self.pos
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128 elif size < 0:
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129 raise IOError(EINVAL, "Negative size not allowed")
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130 elif size < self.pos:
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131 self.pos = size
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132 self.buf = self.getvalue()[:size]
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133
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134 def write(self, s):
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135 if self.closed:
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136 raise ValueError, "I/O operation on closed file"
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137 if not s: return
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138 # Force s to be a string
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139 s = str(s)
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140 if self.pos > self.len:
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141 self.buflist.append('\0'*(self.pos - self.len))
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142 self.len = self.pos
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143 newpos = self.pos + len(s)
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144 if self.pos < self.len:
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145 if self.buflist:
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146 self.buf += ''.join(self.buflist)
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147 self.buflist = []
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148 self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]]
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149 self.buf = ''
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150 if newpos > self.len:
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151 self.len = newpos
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152 else:
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153 self.buflist.append(s)
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154 self.len = newpos
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155 self.pos = newpos
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156
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157 def writelines(self, list):
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158 self.write(''.join(list))
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159
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160 def flush(self):
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161 if self.closed:
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162 raise ValueError, "I/O operation on closed file"
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163
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164 def getvalue(self):
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165 if self.buflist:
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166 self.buf += ''.join(self.buflist)
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167 self.buflist = []
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168 return self.buf
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169
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170
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171 # A little test suite
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172
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173 def test():
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174 import sys
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175 if sys.argv[1:]:
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176 file = sys.argv[1]
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177 else:
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178 file = '/etc/passwd'
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179 lines = open(file, 'r').readlines()
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180 text = open(file, 'r').read()
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181 f = StringIO()
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182 for line in lines[:-2]:
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183 f.write(line)
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184 f.writelines(lines[-2:])
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185 if f.getvalue() != text:
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186 raise RuntimeError, 'write failed'
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187 length = f.tell()
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188 print 'File length =', length
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189 f.seek(len(lines[0]))
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190 f.write(lines[1])
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191 f.seek(0)
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192 print 'First line =', `f.readline()`
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193 here = f.tell()
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194 line = f.readline()
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195 print 'Second line =', `line`
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196 f.seek(-len(line), 1)
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197 line2 = f.read(len(line))
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198 if line != line2:
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199 raise RuntimeError, 'bad result after seek back'
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200 f.seek(len(line2), 1)
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201 list = f.readlines()
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202 line = list[-1]
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203 f.seek(f.tell() - len(line))
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204 line2 = f.read()
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205 if line != line2:
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206 raise RuntimeError, 'bad result after seek back from EOF'
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207 print 'Read', len(list), 'more lines'
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208 print 'File length =', f.tell()
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209 if f.tell() != length:
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210 raise RuntimeError, 'bad length'
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211 f.close()
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212
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213 if __name__ == '__main__':
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214 test()