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| 1 | +r"""File-like objects that read from or write to a string buffer. | |
| 2 | + | |
| 3 | +This implements (nearly) all stdio methods. | |
| 4 | + | |
| 5 | +f = StringIO() # ready for writing | |
| 6 | +f = StringIO(buf) # ready for reading | |
| 7 | +f.close() # explicitly release resources held | |
| 8 | +flag = f.isatty() # always false | |
| 9 | +pos = f.tell() # get current position | |
| 10 | +f.seek(pos) # set current position | |
| 11 | +f.seek(pos, mode) # mode 0: absolute; 1: relative; 2: relative to EOF | |
| 12 | +buf = f.read() # read until EOF | |
| 13 | +buf = f.read(n) # read up to n bytes | |
| 14 | +buf = f.readline() # read until end of line ('\n') or EOF | |
| 15 | +list = f.readlines()# list of f.readline() results until EOF | |
| 16 | +f.truncate([size]) # truncate file at to at most size (default: current pos) | |
| 17 | +f.write(buf) # write at current position | |
| 18 | +f.writelines(list) # for line in list: f.write(line) | |
| 19 | +f.getvalue() # return whole file's contents as a string | |
| 20 | + | |
| 21 | +Notes: | |
| 22 | +- Using a real file is often faster (but less convenient). | |
| 23 | +- There's also a much faster implementation in C, called cStringIO, but | |
| 24 | + it's not subclassable. | |
| 25 | +- fileno() is left unimplemented so that code which uses it triggers | |
| 26 | + an exception early. | |
| 27 | +- Seeking far beyond EOF and then writing will insert real null | |
| 28 | + bytes that occupy space in the buffer. | |
| 29 | +- There's a simple test set (see end of this file). | |
| 30 | +""" | |
| 31 | +try: | |
| 32 | + from errno import EINVAL | |
| 33 | +except ImportError: | |
| 34 | + EINVAL = 22 | |
| 35 | + | |
| 36 | +__all__ = ["StringIO"] | |
| 37 | + | |
| 38 | +def _complain_ifclosed(closed): | |
| 39 | + if closed: | |
| 40 | + raise ValueError, "I/O operation on closed file" | |
| 41 | + | |
| 42 | +class StringIO: | |
| 43 | + """class StringIO([buffer]) | |
| 44 | + | |
| 45 | + When a StringIO object is created, it can be initialized to an existing | |
| 46 | + string by passing the string to the constructor. If no string is given, | |
| 47 | + the StringIO will start empty. | |
| 48 | + | |
| 49 | + The StringIO object can accept either Unicode or 8-bit strings, but | |
| 50 | + mixing the two may take some care. If both are used, 8-bit strings that | |
| 51 | + cannot be interpreted as 7-bit ASCII (that use the 8th bit) will cause | |
| 52 | + a UnicodeError to be raised when getvalue() is called. | |
| 53 | + """ | |
| 54 | + def __init__(self, buf = ''): | |
| 55 | + # Force self.buf to be a string or unicode | |
| 56 | + if not isinstance(buf, basestring): | |
| 57 | + buf = str(buf) | |
| 58 | + self.buf = buf | |
| 59 | + self.len = len(buf) | |
| 60 | + self.buflist = [] | |
| 61 | + self.pos = 0 | |
| 62 | + self.closed = False | |
| 63 | + self.softspace = 0 | |
| 64 | + | |
| 65 | + def __iter__(self): | |
| 66 | + return self | |
| 67 | + | |
| 68 | + def next(self): | |
| 69 | + """A file object is its own iterator, for example iter(f) returns f | |
| 70 | + (unless f is closed). When a file is used as an iterator, typically | |
| 71 | + in a for loop (for example, for line in f: print line), the next() | |
| 72 | + method is called repeatedly. This method returns the next input line, | |
| 73 | + or raises StopIteration when EOF is hit. | |
| 74 | + """ | |
| 75 | + _complain_ifclosed(self.closed) | |
| 76 | + r = self.readline() | |
| 77 | + if not r: | |
| 78 | + raise StopIteration | |
| 79 | + return r | |
| 80 | + | |
| 81 | + def close(self): | |
| 82 | + """Free the memory buffer. | |
| 83 | + """ | |
| 84 | + if not self.closed: | |
| 85 | + self.closed = True | |
| 86 | + del self.buf, self.pos | |
| 87 | + | |
| 88 | + def isatty(self): | |
| 89 | + """Returns False because StringIO objects are not connected to a | |
| 90 | + tty-like device. | |
| 91 | + """ | |
| 92 | + _complain_ifclosed(self.closed) | |
| 93 | + return False | |
| 94 | + | |
| 95 | + def seek(self, pos, mode = 0): | |
| 96 | + """Set the file's current position. | |
| 97 | + | |
| 98 | + The mode argument is optional and defaults to 0 (absolute file | |
| 99 | + positioning); other values are 1 (seek relative to the current | |
| 100 | + position) and 2 (seek relative to the file's end). | |
| 101 | + | |
| 102 | + There is no return value. | |
| 103 | + """ | |
| 104 | + _complain_ifclosed(self.closed) | |
| 105 | + if self.buflist: | |
| 106 | + self.buf += ''.join(self.buflist) | |
| 107 | + self.buflist = [] | |
| 108 | + if mode == 1: | |
| 109 | + pos += self.pos | |
| 110 | + elif mode == 2: | |
| 111 | + pos += self.len | |
| 112 | + self.pos = max(0, pos) | |
| 113 | + | |
| 114 | + def tell(self): | |
| 115 | + """Return the file's current position.""" | |
| 116 | + _complain_ifclosed(self.closed) | |
| 117 | + return self.pos | |
| 118 | + | |
| 119 | + def read(self, n = -1): | |
| 120 | + """Read at most size bytes from the file | |
| 121 | + (less if the read hits EOF before obtaining size bytes). | |
| 122 | + | |
| 123 | + If the size argument is negative or omitted, read all data until EOF | |
| 124 | + is reached. The bytes are returned as a string object. An empty | |
| 125 | + string is returned when EOF is encountered immediately. | |
| 126 | + """ | |
| 127 | + _complain_ifclosed(self.closed) | |
| 128 | + if self.buflist: | |
| 129 | + self.buf += ''.join(self.buflist) | |
| 130 | + self.buflist = [] | |
| 131 | + if n < 0: | |
| 132 | + newpos = self.len | |
| 133 | + else: | |
| 134 | + newpos = min(self.pos+n, self.len) | |
| 135 | + r = self.buf[self.pos:newpos] | |
| 136 | + self.pos = newpos | |
| 137 | + return r | |
| 138 | + | |
| 139 | + def readline(self, length=None): | |
| 140 | + r"""Read one entire line from the file. | |
| 141 | + | |
| 142 | + A trailing newline character is kept in the string (but may be absent | |
| 143 | + when a file ends with an incomplete line). If the size argument is | |
| 144 | + present and non-negative, it is a maximum byte count (including the | |
| 145 | + trailing newline) and an incomplete line may be returned. | |
| 146 | + | |
| 147 | + An empty string is returned only when EOF is encountered immediately. | |
| 148 | + | |
| 149 | + Note: Unlike stdio's fgets(), the returned string contains null | |
| 150 | + characters ('\0') if they occurred in the input. | |
| 151 | + """ | |
| 152 | + _complain_ifclosed(self.closed) | |
| 153 | + if self.buflist: | |
| 154 | + self.buf += ''.join(self.buflist) | |
| 155 | + self.buflist = [] | |
| 156 | + i = self.buf.find('\n', self.pos) | |
| 157 | + if i < 0: | |
| 158 | + newpos = self.len | |
| 159 | + else: | |
| 160 | + newpos = i+1 | |
| 161 | + if length is not None: | |
| 162 | + if self.pos + length < newpos: | |
| 163 | + newpos = self.pos + length | |
| 164 | + r = self.buf[self.pos:newpos] | |
| 165 | + self.pos = newpos | |
| 166 | + return r | |
| 167 | + | |
| 168 | + def readlines(self, sizehint = 0): | |
| 169 | + """Read until EOF using readline() and return a list containing the | |
| 170 | + lines thus read. | |
| 171 | + | |
| 172 | + If the optional sizehint argument is present, instead of reading up | |
| 173 | + to EOF, whole lines totalling approximately sizehint bytes (or more | |
| 174 | + to accommodate a final whole line). | |
| 175 | + """ | |
| 176 | + total = 0 | |
| 177 | + lines = [] | |
| 178 | + line = self.readline() | |
| 179 | + while line: | |
| 180 | + lines.append(line) | |
| 181 | + total += len(line) | |
| 182 | + if 0 < sizehint <= total: | |
| 183 | + break | |
| 184 | + line = self.readline() | |
| 185 | + return lines | |
| 186 | + | |
| 187 | + def truncate(self, size=None): | |
| 188 | + """Truncate the file's size. | |
| 189 | + | |
| 190 | + If the optional size argument is present, the file is truncated to | |
| 191 | + (at most) that size. The size defaults to the current position. | |
| 192 | + The current file position is not changed unless the position | |
| 193 | + is beyond the new file size. | |
| 194 | + | |
| 195 | + If the specified size exceeds the file's current size, the | |
| 196 | + file remains unchanged. | |
| 197 | + """ | |
| 198 | + _complain_ifclosed(self.closed) | |
| 199 | + if size is None: | |
| 200 | + size = self.pos | |
| 201 | + elif size < 0: | |
| 202 | + raise IOError(EINVAL, "Negative size not allowed") | |
| 203 | + elif size < self.pos: | |
| 204 | + self.pos = size | |
| 205 | + self.buf = self.getvalue()[:size] | |
| 206 | + self.len = size | |
| 207 | + | |
| 208 | + def write(self, s): | |
| 209 | + """Write a string to the file. | |
| 210 | + | |
| 211 | + There is no return value. | |
| 212 | + """ | |
| 213 | + _complain_ifclosed(self.closed) | |
| 214 | + if not s: return | |
| 215 | + # Force s to be a string or unicode | |
| 216 | + if not isinstance(s, basestring): | |
| 217 | + s = str(s) | |
| 218 | + spos = self.pos | |
| 219 | + slen = self.len | |
| 220 | + if spos == slen: | |
| 221 | + self.buflist.append(s) | |
| 222 | + self.len = self.pos = spos + len(s) | |
| 223 | + return | |
| 224 | + if spos > slen: | |
| 225 | + self.buflist.append('\0'*(spos - slen)) | |
| 226 | + slen = spos | |
| 227 | + newpos = spos + len(s) | |
| 228 | + if spos < slen: | |
| 229 | + if self.buflist: | |
| 230 | + self.buf += ''.join(self.buflist) | |
| 231 | + self.buflist = [self.buf[:spos], s, self.buf[newpos:]] | |
| 232 | + self.buf = '' | |
| 233 | + if newpos > slen: | |
| 234 | + slen = newpos | |
| 235 | + else: | |
| 236 | + self.buflist.append(s) | |
| 237 | + slen = newpos | |
| 238 | + self.len = slen | |
| 239 | + self.pos = newpos | |
| 240 | + | |
| 241 | + def writelines(self, iterable): | |
| 242 | + """Write a sequence of strings to the file. The sequence can be any | |
| 243 | + iterable object producing strings, typically a list of strings. There | |
| 244 | + is no return value. | |
| 245 | + | |
| 246 | + (The name is intended to match readlines(); writelines() does not add | |
| 247 | + line separators.) | |
| 248 | + """ | |
| 249 | + write = self.write | |
| 250 | + for line in iterable: | |
| 251 | + write(line) | |
| 252 | + | |
| 253 | + def flush(self): | |
| 254 | + """Flush the internal buffer | |
| 255 | + """ | |
| 256 | + _complain_ifclosed(self.closed) | |
| 257 | + | |
| 258 | + def getvalue(self): | |
| 259 | + """ | |
| 260 | + Retrieve the entire contents of the "file" at any time before | |
| 261 | + the StringIO object's close() method is called. | |
| 262 | + | |
| 263 | + The StringIO object can accept either Unicode or 8-bit strings, | |
| 264 | + but mixing the two may take some care. If both are used, 8-bit | |
| 265 | + strings that cannot be interpreted as 7-bit ASCII (that use the | |
| 266 | + 8th bit) will cause a UnicodeError to be raised when getvalue() | |
| 267 | + is called. | |
| 268 | + """ | |
| 269 | + if self.buflist: | |
| 270 | + self.buf += ''.join(self.buflist) | |
| 271 | + self.buflist = [] | |
| 272 | + return self.buf | |
| 273 | + | |
| 274 | + | |
| 275 | +# A little test suite | |
| 276 | + | |
| 277 | +def test(): | |
| 278 | + import sys | |
| 279 | + if sys.argv[1:]: | |
| 280 | + file = sys.argv[1] | |
| 281 | + else: | |
| 282 | + file = '/etc/passwd' | |
| 283 | + lines = open(file, 'r').readlines() | |
| 284 | + text = open(file, 'r').read() | |
| 285 | + f = StringIO() | |
| 286 | + for line in lines[:-2]: | |
| 287 | + f.write(line) | |
| 288 | + f.writelines(lines[-2:]) | |
| 289 | + if f.getvalue() != text: | |
| 290 | + raise RuntimeError, 'write failed' | |
| 291 | + length = f.tell() | |
| 292 | + print 'File length =', length | |
| 293 | + f.seek(len(lines[0])) | |
| 294 | + f.write(lines[1]) | |
| 295 | + f.seek(0) | |
| 296 | + print 'First line =', repr(f.readline()) | |
| 297 | + print 'Position =', f.tell() | |
| 298 | + line = f.readline() | |
| 299 | + print 'Second line =', repr(line) | |
| 300 | + f.seek(-len(line), 1) | |
| 301 | + line2 = f.read(len(line)) | |
| 302 | + if line != line2: | |
| 303 | + raise RuntimeError, 'bad result after seek back' | |
| 304 | + f.seek(len(line2), 1) | |
| 305 | + list = f.readlines() | |
| 306 | + line = list[-1] | |
| 307 | + f.seek(f.tell() - len(line)) | |
| 308 | + line2 = f.read() | |
| 309 | + if line != line2: | |
| 310 | + raise RuntimeError, 'bad result after seek back from EOF' | |
| 311 | + print 'Read', len(list), 'more lines' | |
| 312 | + print 'File length =', f.tell() | |
| 313 | + if f.tell() != length: | |
| 314 | + raise RuntimeError, 'bad length' | |
| 315 | + f.truncate(length/2) | |
| 316 | + f.seek(0, 2) | |
| 317 | + print 'Truncated length =', f.tell() | |
| 318 | + if f.tell() != length/2: | |
| 319 | + raise RuntimeError, 'truncate did not adjust length' | |
| 320 | + f.close() | |
| 321 | + | |
| 322 | +if __name__ == '__main__': | |
| 323 | + test() | |