Mercurial > cpython-lru_cache-weakref

annotate Lib/StringIO.py @ 12357:5b59ea41db4e legacy-trunk

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Install the docs (with fewer rules). Add descriptions for the system variables.
author Guido van Rossum <guido@python.org>
date Mon, 10 Apr 2000 19:36:27 +0000
parents d7eca5b0960a
children e2d62d747f7a
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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.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 - Using a real file is often faster (but less convenient).
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22 - There's also a much faster implementation in C, called cStringIO, but
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23 it's not subclassable.
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24 - fileno() is left unimplemented so that code which uses it triggers
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25 an exception early.
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26 - Seeking far beyond EOF and then writing will insert real null
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27 bytes that occupy space in the buffer.
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28 - There's a simple test set (see end of this file).
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29 """
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30
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31 import string
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32
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33 class StringIO:
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34 def __init__(self, buf = ''):
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35 self.buf = buf
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36 self.len = len(buf)
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37 self.buflist = []
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38 self.pos = 0
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39 self.closed = 0
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40 self.softspace = 0
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41 def close(self):
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42 if not self.closed:
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43 self.closed = 1
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44 del self.buf, self.pos
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45 def isatty(self):
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46 if self.closed:
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47 raise ValueError, "I/O operation on closed file"
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48 return 0
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49 def seek(self, pos, mode = 0):
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50 if self.closed:
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51 raise ValueError, "I/O operation on closed file"
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52 if self.buflist:
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53 self.buf = self.buf + string.joinfields(self.buflist, '')
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54 self.buflist = []
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55 if mode == 1:
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56 pos = pos + self.pos
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57 elif mode == 2:
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58 pos = pos + self.len
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59 self.pos = max(0, pos)
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60 def tell(self):
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61 if self.closed:
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62 raise ValueError, "I/O operation on closed file"
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63 return self.pos
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64 def read(self, n = -1):
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65 if self.closed:
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66 raise ValueError, "I/O operation on closed file"
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67 if self.buflist:
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68 self.buf = self.buf + string.joinfields(self.buflist, '')
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69 self.buflist = []
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70 if n < 0:
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71 newpos = self.len
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72 else:
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73 newpos = min(self.pos+n, self.len)
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74 r = self.buf[self.pos:newpos]
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75 self.pos = newpos
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76 return r
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77 def readline(self, length=None):
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78 if self.closed:
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79 raise ValueError, "I/O operation on closed file"
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80 if self.buflist:
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81 self.buf = self.buf + string.joinfields(self.buflist, '')
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82 self.buflist = []
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83 i = string.find(self.buf, '\n', self.pos)
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84 if i < 0:
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85 newpos = self.len
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86 else:
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87 newpos = i+1
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88 if length is not None:
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89 if self.pos + length < newpos:
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90 newpos = self.pos + length
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91 r = self.buf[self.pos:newpos]
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92 self.pos = newpos
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93 return r
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94 def readlines(self):
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95 lines = []
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96 line = self.readline()
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97 while line:
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98 lines.append(line)
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99 line = self.readline()
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100 return lines
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101 def write(self, s):
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102 if self.closed:
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103 raise ValueError, "I/O operation on closed file"
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104 if not s: return
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105 if self.pos > self.len:
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106 self.buflist.append('\0'*(self.pos - self.len))
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107 self.len = self.pos
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108 newpos = self.pos + len(s)
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109 if self.pos < self.len:
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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 self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]]
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114 self.buf = ''
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115 else:
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116 self.buflist.append(s)
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117 self.len = newpos
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118 self.pos = newpos
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119 def writelines(self, list):
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120 self.write(string.joinfields(list, ''))
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121 def flush(self):
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122 if self.closed:
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123 raise ValueError, "I/O operation on closed file"
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124 def getvalue(self):
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125 if self.buflist:
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126 self.buf = self.buf + string.joinfields(self.buflist, '')
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127 self.buflist = []
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128 return self.buf
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129
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130
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131 # A little test suite
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132
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133 def test():
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134 import sys
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135 if sys.argv[1:]:
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136 file = sys.argv[1]
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137 else:
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138 file = '/etc/passwd'
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139 lines = open(file, 'r').readlines()
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140 text = open(file, 'r').read()
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141 f = StringIO()
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142 for line in lines[:-2]:
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143 f.write(line)
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144 f.writelines(lines[-2:])
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145 if f.getvalue() != text:
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146 raise RuntimeError, 'write failed'
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147 length = f.tell()
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148 print 'File length =', length
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149 f.seek(len(lines[0]))
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150 f.write(lines[1])
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151 f.seek(0)
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152 print 'First line =', `f.readline()`
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153 here = f.tell()
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154 line = f.readline()
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155 print 'Second line =', `line`
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156 f.seek(-len(line), 1)
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157 line2 = f.read(len(line))
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158 if line != line2:
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159 raise RuntimeError, 'bad result after seek back'
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160 f.seek(len(line2), 1)
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161 list = f.readlines()
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162 line = list[-1]
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163 f.seek(f.tell() - len(line))
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164 line2 = f.read()
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165 if line != line2:
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166 raise RuntimeError, 'bad result after seek back from EOF'
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167 print 'Read', len(list), 'more lines'
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168 print 'File length =', f.tell()
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169 if f.tell() != length:
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170 raise RuntimeError, 'bad length'
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171 f.close()
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172
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173 if __name__ == '__main__':
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174 test()