Mercurial > cpython-lru_cache-weakref

annotate Lib/StringIO.py @ 80661:94de77bd0b4b 2.7

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Issue #16194: document imp.load_dynamic problems when read several extension modules from the same binary object file.
author Andrew Svetlov <andrew.svetlov@gmail.com>
date Thu, 29 Nov 2012 19:51:28 +0200
parents 720804a91c01
children 7513bd184a01
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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292ad135cef1 Make the module docstring a raw string, so that the backslash in
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1 r"""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 try:
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32 from errno import EINVAL
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33 except ImportError:
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34 EINVAL = 22
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35
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36 __all__ = ["StringIO"]
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37
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38 def _complain_ifclosed(closed):
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39 if closed:
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40 raise ValueError, "I/O operation on closed file"
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41
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42 class StringIO:
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43 """class StringIO([buffer])
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44
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45 When a StringIO object is created, it can be initialized to an existing
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46 string by passing the string to the constructor. If no string is given,
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47 the StringIO will start empty.
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48
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49 The StringIO object can accept either Unicode or 8-bit strings, but
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50 mixing the two may take some care. If both are used, 8-bit strings that
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51 cannot be interpreted as 7-bit ASCII (that use the 8th bit) will cause
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52 a UnicodeError to be raised when getvalue() is called.
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53 """
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54 def __init__(self, buf = ''):
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55 # Force self.buf to be a string or unicode
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56 if not isinstance(buf, basestring):
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57 buf = str(buf)
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58 self.buf = buf
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59 self.len = len(buf)
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60 self.buflist = []
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61 self.pos = 0
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62 self.closed = False
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63 self.softspace = 0
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64
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65 def __iter__(self):
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66 return self
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67
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68 def next(self):
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69 """A file object is its own iterator, for example iter(f) returns f
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70 (unless f is closed). When a file is used as an iterator, typically
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71 in a for loop (for example, for line in f: print line), the next()
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72 method is called repeatedly. This method returns the next input line,
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73 or raises StopIteration when EOF is hit.
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74 """
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75 _complain_ifclosed(self.closed)
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76 r = self.readline()
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77 if not r:
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78 raise StopIteration
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79 return r
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80
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81 def close(self):
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82 """Free the memory buffer.
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83 """
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84 if not self.closed:
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85 self.closed = True
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86 del self.buf, self.pos
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87
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88 def isatty(self):
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89 """Returns False because StringIO objects are not connected to a
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90 tty-like device.
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91 """
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92 _complain_ifclosed(self.closed)
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93 return False
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94
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95 def seek(self, pos, mode = 0):
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96 """Set the file's current position.
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97
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98 The mode argument is optional and defaults to 0 (absolute file
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99 positioning); other values are 1 (seek relative to the current
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100 position) and 2 (seek relative to the file's end).
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101
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102 There is no return value.
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103 """
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104 _complain_ifclosed(self.closed)
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105 if self.buflist:
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106 self.buf += ''.join(self.buflist)
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107 self.buflist = []
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108 if mode == 1:
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109 pos += self.pos
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110 elif mode == 2:
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111 pos += self.len
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112 self.pos = max(0, pos)
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113
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114 def tell(self):
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115 """Return the file's current position."""
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116 _complain_ifclosed(self.closed)
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117 return self.pos
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118
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119 def read(self, n = -1):
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120 """Read at most size bytes from the file
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121 (less if the read hits EOF before obtaining size bytes).
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122
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123 If the size argument is negative or omitted, read all data until EOF
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124 is reached. The bytes are returned as a string object. An empty
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125 string is returned when EOF is encountered immediately.
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126 """
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127 _complain_ifclosed(self.closed)
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128 if self.buflist:
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129 self.buf += ''.join(self.buflist)
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130 self.buflist = []
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131 if n is None or n < 0:
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132 newpos = self.len
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133 else:
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134 newpos = min(self.pos+n, self.len)
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135 r = self.buf[self.pos:newpos]
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136 self.pos = newpos
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137 return r
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138
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139 def readline(self, length=None):
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140 r"""Read one entire line from the file.
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141
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142 A trailing newline character is kept in the string (but may be absent
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143 when a file ends with an incomplete line). If the size argument is
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144 present and non-negative, it is a maximum byte count (including the
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145 trailing newline) and an incomplete line may be returned.
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146
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147 An empty string is returned only when EOF is encountered immediately.
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148
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149 Note: Unlike stdio's fgets(), the returned string contains null
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150 characters ('\0') if they occurred in the input.
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151 """
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152 _complain_ifclosed(self.closed)
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153 if self.buflist:
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154 self.buf += ''.join(self.buflist)
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155 self.buflist = []
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156 i = self.buf.find('\n', self.pos)
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157 if i < 0:
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158 newpos = self.len
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159 else:
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160 newpos = i+1
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161 if length is not None and length > 0:
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162 if self.pos + length < newpos:
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163 newpos = self.pos + length
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164 r = self.buf[self.pos:newpos]
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165 self.pos = newpos
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166 return r
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167
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168 def readlines(self, sizehint = 0):
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169 """Read until EOF using readline() and return a list containing the
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170 lines thus read.
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171
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172 If the optional sizehint argument is present, instead of reading up
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173 to EOF, whole lines totalling approximately sizehint bytes (or more
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174 to accommodate a final whole line).
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175 """
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176 total = 0
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177 lines = []
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178 line = self.readline()
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179 while line:
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180 lines.append(line)
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181 total += len(line)
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182 if 0 < sizehint <= total:
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183 break
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184 line = self.readline()
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185 return lines
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186
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187 def truncate(self, size=None):
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188 """Truncate the file's size.
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189
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190 If the optional size argument is present, the file is truncated to
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191 (at most) that size. The size defaults to the current position.
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192 The current file position is not changed unless the position
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193 is beyond the new file size.
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194
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195 If the specified size exceeds the file's current size, the
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196 file remains unchanged.
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197 """
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198 _complain_ifclosed(self.closed)
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199 if size is None:
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200 size = self.pos
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201 elif size < 0:
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202 raise IOError(EINVAL, "Negative size not allowed")
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203 elif size < self.pos:
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204 self.pos = size
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205 self.buf = self.getvalue()[:size]
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206 self.len = size
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207
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208 def write(self, s):
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209 """Write a string to the file.
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210
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211 There is no return value.
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212 """
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213 _complain_ifclosed(self.closed)
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214 if not s: return
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215 # Force s to be a string or unicode
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216 if not isinstance(s, basestring):
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217 s = str(s)
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218 spos = self.pos
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219 slen = self.len
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220 if spos == slen:
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221 self.buflist.append(s)
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222 self.len = self.pos = spos + len(s)
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223 return
33544
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224 if spos > slen:
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225 self.buflist.append('\0'*(spos - slen))
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226 slen = spos
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227 newpos = spos + len(s)
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228 if spos < slen:
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229 if self.buflist:
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230 self.buf += ''.join(self.buflist)
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231 self.buflist = [self.buf[:spos], s, self.buf[newpos:]]
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232 self.buf = ''
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233 if newpos > slen:
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234 slen = newpos
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235 else:
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236 self.buflist.append(s)
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diff changeset
237 slen = newpos
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238 self.len = slen
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239 self.pos = newpos
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240
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241 def writelines(self, iterable):
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242 """Write a sequence of strings to the file. The sequence can be any
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243 iterable object producing strings, typically a list of strings. There
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244 is no return value.
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245
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246 (The name is intended to match readlines(); writelines() does not add
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247 line separators.)
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248 """
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diff changeset
249 write = self.write
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diff changeset
250 for line in iterable:
1543afab1b67 SF patch #907403: Improvements to cStringIO.writelines()
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251 write(line)
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252
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253 def flush(self):
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254 """Flush the internal buffer
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255 """
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diff changeset
256 _complain_ifclosed(self.closed)
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257
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258 def getvalue(self):
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diff changeset
259 """
68c776ba5ea5 Added docstrings excerpted from Python Library Reference.
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diff changeset
260 Retrieve the entire contents of the "file" at any time before
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diff changeset
261 the StringIO object's close() method is called.
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diff changeset
262
68c776ba5ea5 Added docstrings excerpted from Python Library Reference.
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parents: 23432
diff changeset
263 The StringIO object can accept either Unicode or 8-bit strings,
68c776ba5ea5 Added docstrings excerpted from Python Library Reference.
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parents: 23432
diff changeset
264 but mixing the two may take some care. If both are used, 8-bit
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diff changeset
265 strings that cannot be interpreted as 7-bit ASCII (that use the
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diff changeset
266 8th bit) will cause a UnicodeError to be raised when getvalue()
23521
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267 is called.
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diff changeset
268 """
70425
720804a91c01 raise an ValueError in getvalue() on closed StringIO (closes #12161)
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parents: 68256
diff changeset
269 _complain_ifclosed(self.closed)
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diff changeset
270 if self.buflist:
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diff changeset
271 self.buf += ''.join(self.buflist)
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272 self.buflist = []
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diff changeset
273 return self.buf
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274
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275
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276 # A little test suite
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277
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278 def test():
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279 import sys
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280 if sys.argv[1:]:
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281 file = sys.argv[1]
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282 else:
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283 file = '/etc/passwd'
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284 lines = open(file, 'r').readlines()
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285 text = open(file, 'r').read()
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286 f = StringIO()
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287 for line in lines[:-2]:
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288 f.write(line)
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289 f.writelines(lines[-2:])
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290 if f.getvalue() != text:
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291 raise RuntimeError, 'write failed'
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292 length = f.tell()
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293 print 'File length =', length
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294 f.seek(len(lines[0]))
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295 f.write(lines[1])
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296 f.seek(0)
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297 print 'First line =', repr(f.readline())
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298 print 'Position =', f.tell()
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299 line = f.readline()
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300 print 'Second line =', repr(line)
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301 f.seek(-len(line), 1)
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302 line2 = f.read(len(line))
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303 if line != line2:
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304 raise RuntimeError, 'bad result after seek back'
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305 f.seek(len(line2), 1)
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306 list = f.readlines()
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307 line = list[-1]
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308 f.seek(f.tell() - len(line))
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309 line2 = f.read()
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310 if line != line2:
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311 raise RuntimeError, 'bad result after seek back from EOF'
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312 print 'Read', len(list), 'more lines'
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313 print 'File length =', f.tell()
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314 if f.tell() != length:
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315 raise RuntimeError, 'bad length'
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316 f.truncate(length/2)
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317 f.seek(0, 2)
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318 print 'Truncated length =', f.tell()
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319 if f.tell() != length/2:
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320 raise RuntimeError, 'truncate did not adjust length'
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321 f.close()
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322
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323 if __name__ == '__main__':
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324 test()