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920dae64 AT |
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 | if self.closed: | |
76 | raise StopIteration | |
77 | r = self.readline() | |
78 | if not r: | |
79 | raise StopIteration | |
80 | return r | |
81 | ||
82 | def close(self): | |
83 | """Free the memory buffer. | |
84 | """ | |
85 | if not self.closed: | |
86 | self.closed = True | |
87 | del self.buf, self.pos | |
88 | ||
89 | def isatty(self): | |
90 | """Returns False because StringIO objects are not connected to a | |
91 | tty-like device. | |
92 | """ | |
93 | _complain_ifclosed(self.closed) | |
94 | return False | |
95 | ||
96 | def seek(self, pos, mode = 0): | |
97 | """Set the file's current position. | |
98 | ||
99 | The mode argument is optional and defaults to 0 (absolute file | |
100 | positioning); other values are 1 (seek relative to the current | |
101 | position) and 2 (seek relative to the file's end). | |
102 | ||
103 | There is no return value. | |
104 | """ | |
105 | _complain_ifclosed(self.closed) | |
106 | if self.buflist: | |
107 | self.buf += ''.join(self.buflist) | |
108 | self.buflist = [] | |
109 | if mode == 1: | |
110 | pos += self.pos | |
111 | elif mode == 2: | |
112 | pos += self.len | |
113 | self.pos = max(0, pos) | |
114 | ||
115 | def tell(self): | |
116 | """Return the file's current position.""" | |
117 | _complain_ifclosed(self.closed) | |
118 | return self.pos | |
119 | ||
120 | def read(self, n = -1): | |
121 | """Read at most size bytes from the file | |
122 | (less if the read hits EOF before obtaining size bytes). | |
123 | ||
124 | If the size argument is negative or omitted, read all data until EOF | |
125 | is reached. The bytes are returned as a string object. An empty | |
126 | string is returned when EOF is encountered immediately. | |
127 | """ | |
128 | _complain_ifclosed(self.closed) | |
129 | if self.buflist: | |
130 | self.buf += ''.join(self.buflist) | |
131 | self.buflist = [] | |
132 | if n < 0: | |
133 | newpos = self.len | |
134 | else: | |
135 | newpos = min(self.pos+n, self.len) | |
136 | r = self.buf[self.pos:newpos] | |
137 | self.pos = newpos | |
138 | return r | |
139 | ||
140 | def readline(self, length=None): | |
141 | """Read one entire line from the file. | |
142 | ||
143 | A trailing newline character is kept in the string (but may be absent | |
144 | when a file ends with an incomplete line). If the size argument is | |
145 | present and non-negative, it is a maximum byte count (including the | |
146 | trailing newline) and an incomplete line may be returned. | |
147 | ||
148 | An empty string is returned only when EOF is encountered immediately. | |
149 | ||
150 | Note: Unlike stdio's fgets(), the returned string contains null | |
151 | characters ('\0') if they occurred in the input. | |
152 | """ | |
153 | _complain_ifclosed(self.closed) | |
154 | if self.buflist: | |
155 | self.buf += ''.join(self.buflist) | |
156 | self.buflist = [] | |
157 | i = self.buf.find('\n', self.pos) | |
158 | if i < 0: | |
159 | newpos = self.len | |
160 | else: | |
161 | newpos = i+1 | |
162 | if length is not None: | |
163 | if self.pos + length < newpos: | |
164 | newpos = self.pos + length | |
165 | r = self.buf[self.pos:newpos] | |
166 | self.pos = newpos | |
167 | return r | |
168 | ||
169 | def readlines(self, sizehint = 0): | |
170 | """Read until EOF using readline() and return a list containing the | |
171 | lines thus read. | |
172 | ||
173 | If the optional sizehint argument is present, instead of reading up | |
174 | to EOF, whole lines totalling approximately sizehint bytes (or more | |
175 | to accommodate a final whole line). | |
176 | """ | |
177 | total = 0 | |
178 | lines = [] | |
179 | line = self.readline() | |
180 | while line: | |
181 | lines.append(line) | |
182 | total += len(line) | |
183 | if 0 < sizehint <= total: | |
184 | break | |
185 | line = self.readline() | |
186 | return lines | |
187 | ||
188 | def truncate(self, size=None): | |
189 | """Truncate the file's size. | |
190 | ||
191 | If the optional size argument is present, the file is truncated to | |
192 | (at most) that size. The size defaults to the current position. | |
193 | The current file position is not changed unless the position | |
194 | is beyond the new file size. | |
195 | ||
196 | If the specified size exceeds the file's current size, the | |
197 | file remains unchanged. | |
198 | """ | |
199 | _complain_ifclosed(self.closed) | |
200 | if size is None: | |
201 | size = self.pos | |
202 | elif size < 0: | |
203 | raise IOError(EINVAL, "Negative size not allowed") | |
204 | elif size < self.pos: | |
205 | self.pos = size | |
206 | self.buf = self.getvalue()[:size] | |
207 | self.len = size | |
208 | ||
209 | def write(self, s): | |
210 | """Write a string to the file. | |
211 | ||
212 | There is no return value. | |
213 | """ | |
214 | _complain_ifclosed(self.closed) | |
215 | if not s: return | |
216 | # Force s to be a string or unicode | |
217 | if not isinstance(s, basestring): | |
218 | s = str(s) | |
219 | spos = self.pos | |
220 | slen = self.len | |
221 | if spos == slen: | |
222 | self.buflist.append(s) | |
223 | self.len = self.pos = spos + len(s) | |
224 | return | |
225 | if spos > slen: | |
226 | self.buflist.append('\0'*(spos - slen)) | |
227 | slen = spos | |
228 | newpos = spos + len(s) | |
229 | if spos < slen: | |
230 | if self.buflist: | |
231 | self.buf += ''.join(self.buflist) | |
232 | self.buflist = [self.buf[:spos], s, self.buf[newpos:]] | |
233 | self.buf = '' | |
234 | if newpos > slen: | |
235 | slen = newpos | |
236 | else: | |
237 | self.buflist.append(s) | |
238 | slen = newpos | |
239 | self.len = slen | |
240 | self.pos = newpos | |
241 | ||
242 | def writelines(self, iterable): | |
243 | """Write a sequence of strings to the file. The sequence can be any | |
244 | iterable object producing strings, typically a list of strings. There | |
245 | is no return value. | |
246 | ||
247 | (The name is intended to match readlines(); writelines() does not add | |
248 | line separators.) | |
249 | """ | |
250 | write = self.write | |
251 | for line in iterable: | |
252 | write(line) | |
253 | ||
254 | def flush(self): | |
255 | """Flush the internal buffer | |
256 | """ | |
257 | _complain_ifclosed(self.closed) | |
258 | ||
259 | def getvalue(self): | |
260 | """ | |
261 | Retrieve the entire contents of the "file" at any time before | |
262 | the StringIO object's close() method is called. | |
263 | ||
264 | The StringIO object can accept either Unicode or 8-bit strings, | |
265 | but mixing the two may take some care. If both are used, 8-bit | |
266 | strings that cannot be interpreted as 7-bit ASCII (that use the | |
267 | 8th bit) will cause a UnicodeError to be raised when getvalue() | |
268 | is called. | |
269 | """ | |
270 | if self.buflist: | |
271 | self.buf += ''.join(self.buflist) | |
272 | self.buflist = [] | |
273 | return self.buf | |
274 | ||
275 | ||
276 | # A little test suite | |
277 | ||
278 | def test(): | |
279 | import sys | |
280 | if sys.argv[1:]: | |
281 | file = sys.argv[1] | |
282 | else: | |
283 | file = '/etc/passwd' | |
284 | lines = open(file, 'r').readlines() | |
285 | text = open(file, 'r').read() | |
286 | f = StringIO() | |
287 | for line in lines[:-2]: | |
288 | f.write(line) | |
289 | f.writelines(lines[-2:]) | |
290 | if f.getvalue() != text: | |
291 | raise RuntimeError, 'write failed' | |
292 | length = f.tell() | |
293 | print 'File length =', length | |
294 | f.seek(len(lines[0])) | |
295 | f.write(lines[1]) | |
296 | f.seek(0) | |
297 | print 'First line =', repr(f.readline()) | |
298 | print 'Position =', f.tell() | |
299 | line = f.readline() | |
300 | print 'Second line =', repr(line) | |
301 | f.seek(-len(line), 1) | |
302 | line2 = f.read(len(line)) | |
303 | if line != line2: | |
304 | raise RuntimeError, 'bad result after seek back' | |
305 | f.seek(len(line2), 1) | |
306 | list = f.readlines() | |
307 | line = list[-1] | |
308 | f.seek(f.tell() - len(line)) | |
309 | line2 = f.read() | |
310 | if line != line2: | |
311 | raise RuntimeError, 'bad result after seek back from EOF' | |
312 | print 'Read', len(list), 'more lines' | |
313 | print 'File length =', f.tell() | |
314 | if f.tell() != length: | |
315 | raise RuntimeError, 'bad length' | |
316 | f.truncate(length/2) | |
317 | f.seek(0, 2) | |
318 | print 'Truncated length =', f.tell() | |
319 | if f.tell() != length/2: | |
320 | raise RuntimeError, 'truncate did not adjust length' | |
321 | f.close() | |
322 | ||
323 | if __name__ == '__main__': | |
324 | test() |