Mercurial > cpython-lru_cache-weakref

annotate Lib/StringIO.py @ 49955:878d40468c4e legacy-trunk

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Issue #4384: Added logging integration with warnings module using captureWarnings(). This change includes a NullHandler which does nothing; it will be of use to library developers who want to avoid the "No handlers could be found for logger XXX" message which can appear if the library user doesn't configure logging.
author Vinay Sajip <vinay_sajip@yahoo.co.uk>
date Wed, 03 Dec 2008 23:22:58 +0000
parents 7f76996c7bf4
children 6052751a04c8 e8532cc8a14e
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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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 < 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:
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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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diff changeset
181 total += len(line)
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diff changeset
182 if 0 < sizehint <= total:
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parents: 15542
diff changeset
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):
31662
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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 """
31389
aca1ce1b4b61 Whitespace normalization.
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parents: 31190
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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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diff changeset
203 elif size < self.pos:
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diff changeset
204 self.pos = size
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diff changeset
205 self.buf = self.getvalue()[:size]
34207
19286994f74f SF bug #951915: fix bug in StringIO.truncate - length not changed
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diff changeset
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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parents: 27550
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213 _complain_ifclosed(self.closed)
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diff changeset
214 if not s: return
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Marc-André Lemburg <mal@egenix.com>
parents: 20060
diff changeset
215 # Force s to be a string or unicode
23645
e1e90b0f1f45 Remove uses of the string and types modules:
Walter Dörwald <walter@livinglogic.de>
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diff changeset
216 if not isinstance(s, basestring):
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217 s = str(s)
33544
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diff changeset
218 spos = self.pos
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219 slen = self.len
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220 if spos == slen:
25305
0399c8aea7b2 write(): Special case the common situation of a stream that's only
Fred Drake <fdrake@acm.org>
parents: 23645
diff changeset
221 self.buflist.append(s)
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diff changeset
222 self.len = self.pos = spos + len(s)
25305
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diff changeset
223 return
33544
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diff changeset
224 if spos > slen:
d6071a05ba84 Use local variables in StringIO.write().
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diff changeset
225 self.buflist.append('\0'*(spos - slen))
d6071a05ba84 Use local variables in StringIO.write().
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diff changeset
226 slen = spos
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diff changeset
227 newpos = spos + len(s)
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diff changeset
228 if spos < slen:
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diff changeset
229 if self.buflist:
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diff changeset
230 self.buf += ''.join(self.buflist)
33544
d6071a05ba84 Use local variables in StringIO.write().
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diff changeset
231 self.buflist = [self.buf[:spos], s, self.buf[newpos:]]
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diff changeset
232 self.buf = ''
33544
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diff changeset
233 if newpos > slen:
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parents: 33544
diff changeset
234 slen = newpos
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235 else:
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diff changeset
236 self.buflist.append(s)
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parents: 33544
diff changeset
237 slen = newpos
6d055a275b4b Arghh, checked in wrong draft. Replacing with correct one.
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parents: 33544
diff changeset
238 self.len = slen
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diff changeset
239 self.pos = newpos
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diff changeset
240
31626
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diff changeset
241 def writelines(self, iterable):
31662
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242 """Write a sequence of strings to the file. The sequence can be any
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Raymond Hettinger <python@rcn.com>
parents: 31626
diff changeset
243 iterable object producing strings, typically a list of strings. There
88e9c0444d4d Add missing docstrings.
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diff changeset
244 is no return value.
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245
88e9c0444d4d Add missing docstrings.
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diff changeset
246 (The name is intended to match readlines(); writelines() does not add
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Raymond Hettinger <python@rcn.com>
parents: 31626
diff changeset
247 line separators.)
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Raymond Hettinger <python@rcn.com>
parents: 31626
diff changeset
248 """
31626
1543afab1b67 SF patch #907403: Improvements to cStringIO.writelines()
Raymond Hettinger <python@rcn.com>
parents: 31515
diff changeset
249 write = self.write
1543afab1b67 SF patch #907403: Improvements to cStringIO.writelines()
Raymond Hettinger <python@rcn.com>
parents: 31515
diff changeset
250 for line in iterable:
1543afab1b67 SF patch #907403: Improvements to cStringIO.writelines()
Raymond Hettinger <python@rcn.com>
parents: 31515
diff changeset
251 write(line)
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diff changeset
252
6359480106ec Change the file's indentation from tabs to 4 spaces per level.
Barry Warsaw <barry@python.org>
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diff changeset
253 def flush(self):
31662
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diff changeset
254 """Flush the internal buffer
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parents: 31626
diff changeset
255 """
30708
3a99294c8e5b Patch #822994: Consolidate tests for self.closed.
Martin v. Löwis <martin@v.loewis.de>
parents: 27550
diff changeset
256 _complain_ifclosed(self.closed)
15542
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diff changeset
257
6359480106ec Change the file's indentation from tabs to 4 spaces per level.
Barry Warsaw <barry@python.org>
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diff changeset
258 def getvalue(self):
23455
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Raymond Hettinger <python@rcn.com>
parents: 23432
diff changeset
259 """
68c776ba5ea5 Added docstrings excerpted from Python Library Reference.
Raymond Hettinger <python@rcn.com>
parents: 23432
diff changeset
260 Retrieve the entire contents of the "file" at any time before
68c776ba5ea5 Added docstrings excerpted from Python Library Reference.
Raymond Hettinger <python@rcn.com>
parents: 23432
diff changeset
261 the StringIO object's close() method is called.
68c776ba5ea5 Added docstrings excerpted from Python Library Reference.
Raymond Hettinger <python@rcn.com>
parents: 23432
diff changeset
262
68c776ba5ea5 Added docstrings excerpted from Python Library Reference.
Raymond Hettinger <python@rcn.com>
parents: 23432
diff changeset
263 The StringIO object can accept either Unicode or 8-bit strings,
68c776ba5ea5 Added docstrings excerpted from Python Library Reference.
Raymond Hettinger <python@rcn.com>
parents: 23432
diff changeset
264 but mixing the two may take some care. If both are used, 8-bit
68c776ba5ea5 Added docstrings excerpted from Python Library Reference.
Raymond Hettinger <python@rcn.com>
parents: 23432
diff changeset
265 strings that cannot be interpreted as 7-bit ASCII (that use the
68c776ba5ea5 Added docstrings excerpted from Python Library Reference.
Raymond Hettinger <python@rcn.com>
parents: 23432
diff changeset
266 8th bit) will cause a UnicodeError to be raised when getvalue()
23521
a90faa5f9417 Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents: 23455
diff changeset
267 is called.
23455
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parents: 23432
diff changeset
268 """
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diff changeset
269 if self.buflist:
16522
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parents: 16070
diff changeset
270 self.buf += ''.join(self.buflist)
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diff changeset
271 self.buflist = []
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diff changeset
272 return self.buf
1680
0a60460e99f0 Two new generally useful modules: types defines names for all built-in types,
Guido van Rossum <guido@python.org>
parents:
diff changeset
273
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274
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275 # A little test suite
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276
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277 def test():
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278 import sys
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279 if sys.argv[1:]:
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280 file = sys.argv[1]
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281 else:
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282 file = '/etc/passwd'
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283 lines = open(file, 'r').readlines()
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284 text = open(file, 'r').read()
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285 f = StringIO()
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286 for line in lines[:-2]:
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287 f.write(line)
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288 f.writelines(lines[-2:])
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289 if f.getvalue() != text:
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290 raise RuntimeError, 'write failed'
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291 length = f.tell()
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292 print 'File length =', length
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293 f.seek(len(lines[0]))
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294 f.write(lines[1])
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295 f.seek(0)
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296 print 'First line =', repr(f.readline())
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297 print 'Position =', f.tell()
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298 line = f.readline()
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299 print 'Second line =', repr(line)
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300 f.seek(-len(line), 1)
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301 line2 = f.read(len(line))
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302 if line != line2:
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303 raise RuntimeError, 'bad result after seek back'
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304 f.seek(len(line2), 1)
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305 list = f.readlines()
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306 line = list[-1]
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307 f.seek(f.tell() - len(line))
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308 line2 = f.read()
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309 if line != line2:
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310 raise RuntimeError, 'bad result after seek back from EOF'
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311 print 'Read', len(list), 'more lines'
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312 print 'File length =', f.tell()
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313 if f.tell() != length:
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314 raise RuntimeError, 'bad length'
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315 f.truncate(length/2)
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316 f.seek(0, 2)
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317 print 'Truncated length =', f.tell()
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318 if f.tell() != length/2:
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319 raise RuntimeError, 'truncate did not adjust length'
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320 f.close()
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321
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322 if __name__ == '__main__':
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323 test()