Mercurial > cpython-lru_cache-weakref

annotate Lib/StringIO.py @ 6719:faebc1940432 legacy-trunk

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author Guido van Rossum <guido@python.org>
date Tue, 02 Dec 1997 20:38:11 +0000
parents 253377a40644
children b9a070736eac
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1 # class StringIO implements file-like objects that read/write a
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2 # string buffer (a.k.a. "memory files").
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3 #
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4 # This implements (nearly) all stdio methods.
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5 #
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6 # f = StringIO() # ready for writing
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7 # f = StringIO(buf) # ready for reading
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8 # f.close() # explicitly release resources held
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9 # flag = f.isatty() # always false
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10 # pos = f.tell() # get current position
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11 # f.seek(pos) # set current position
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12 # f.seek(pos, mode) # mode 0: absolute; 1: relative; 2: relative to EOF
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13 # buf = f.read() # read until EOF
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14 # buf = f.read(n) # read up to n bytes
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15 # buf = f.readline() # read until end of line ('\n') or EOF
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16 # list = f.readlines()# list of f.readline() results until EOF
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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 # - fileno() is left unimplemented so that code which uses it triggers
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24 # an exception early.
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25 # - Seeking far beyond EOF and then writing will insert real null
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26 # bytes that occupy space in the buffer.
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27 # - There's a simple test set (see end of this file).
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28
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29 import string
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30
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31 class StringIO:
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32 def __init__(self, buf = ''):
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33 self.buf = buf
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34 self.len = len(buf)
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35 self.buflist = []
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36 self.pos = 0
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37 self.closed = 0
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38 self.softspace = 0
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39 def close(self):
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40 if not self.closed:
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41 self.closed = 1
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42 del self.buf, self.pos
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43 def isatty(self):
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44 return 0
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45 def seek(self, pos, mode = 0):
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46 if self.buflist:
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47 self.buf = self.buf + string.joinfields(self.buflist, '')
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48 self.buflist = []
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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 + self.len
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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 self.buflist:
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58 self.buf = self.buf + string.joinfields(self.buflist, '')
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59 self.buflist = []
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60 if n < 0:
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61 newpos = self.len
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62 else:
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63 newpos = min(self.pos+n, self.len)
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64 r = self.buf[self.pos:newpos]
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65 self.pos = newpos
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66 return r
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67 def readline(self, length=None):
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68 if self.buflist:
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69 self.buf = self.buf + string.joinfields(self.buflist, '')
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70 self.buflist = []
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71 i = string.find(self.buf, '\n', self.pos)
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72 if i < 0:
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73 newpos = self.len
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74 else:
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75 newpos = i+1
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76 if length is not None:
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77 if self.pos + length < newpos:
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78 newpos = self.pos + length
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79 r = self.buf[self.pos:newpos]
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80 self.pos = newpos
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81 return r
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82 def readlines(self):
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83 lines = []
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84 line = self.readline()
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85 while line:
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86 lines.append(line)
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87 line = self.readline()
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88 return lines
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89 def write(self, s):
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90 if not s: return
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91 if self.pos > self.len:
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92 self.buflist.append('\0'*(self.pos - self.len))
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93 self.len = self.pos
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94 newpos = self.pos + len(s)
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95 if self.pos < self.len:
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96 if self.buflist:
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97 self.buf = self.buf + string.joinfields(self.buflist, '')
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98 self.buflist = []
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99 self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]]
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100 self.buf = ''
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101 else:
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102 self.buflist.append(s)
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103 self.len = newpos
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104 self.pos = newpos
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105 def writelines(self, list):
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106 self.write(string.joinfields(list, ''))
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107 def flush(self):
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108 pass
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109 def getvalue(self):
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110 if self.buflist:
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111 self.buf = self.buf + string.joinfields(self.buflist, '')
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112 self.buflist = []
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113 return self.buf
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114
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115
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116 # A little test suite
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117
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118 def test():
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119 import sys
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120 if sys.argv[1:]:
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121 file = sys.argv[1]
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122 else:
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123 file = '/etc/passwd'
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124 lines = open(file, 'r').readlines()
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125 text = open(file, 'r').read()
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126 f = StringIO()
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127 for line in lines[:-2]:
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128 f.write(line)
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129 f.writelines(lines[-2:])
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130 if f.getvalue() != text:
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131 raise RuntimeError, 'write failed'
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132 length = f.tell()
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133 print 'File length =', length
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134 f.seek(len(lines[0]))
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135 f.write(lines[1])
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136 f.seek(0)
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137 print 'First line =', `f.readline()`
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138 here = f.tell()
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139 line = f.readline()
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140 print 'Second line =', `line`
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141 f.seek(-len(line), 1)
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142 line2 = f.read(len(line))
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143 if line != line2:
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144 raise RuntimeError, 'bad result after seek back'
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145 f.seek(len(line2), 1)
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146 list = f.readlines()
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147 line = list[-1]
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148 f.seek(f.tell() - len(line))
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149 line2 = f.read()
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150 if line != line2:
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151 raise RuntimeError, 'bad result after seek back from EOF'
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152 print 'Read', len(list), 'more lines'
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153 print 'File length =', f.tell()
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154 if f.tell() != length:
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155 raise RuntimeError, 'bad length'
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156 f.close()
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157
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158 if __name__ == '__main__':
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159 test()