blob: 6952b1a999e75edfe6ab5ae3e6cc8048f8f1e6c4 [file] [log] [blame]
Guido van Rossum4acc25b2000-02-02 15:10:15 +00001"""File-like objects that read from or write to a string buffer.
2
3This implements (nearly) all stdio methods.
4
5f = StringIO() # ready for writing
6f = StringIO(buf) # ready for reading
7f.close() # explicitly release resources held
8flag = f.isatty() # always false
9pos = f.tell() # get current position
10f.seek(pos) # set current position
11f.seek(pos, mode) # mode 0: absolute; 1: relative; 2: relative to EOF
12buf = f.read() # read until EOF
13buf = f.read(n) # read up to n bytes
14buf = f.readline() # read until end of line ('\n') or EOF
15list = f.readlines()# list of f.readline() results until EOF
Fred Drakee0a7f4f2000-09-28 04:21:06 +000016f.truncate([size]) # truncate file at to at most size (default: current pos)
Guido van Rossum4acc25b2000-02-02 15:10:15 +000017f.write(buf) # write at current position
18f.writelines(list) # for line in list: f.write(line)
19f.getvalue() # return whole file's contents as a string
20
21Notes:
22- Using a real file is often faster (but less convenient).
Guido van Rossum98d9fd32000-02-28 15:12:25 +000023- There's also a much faster implementation in C, called cStringIO, but
24 it's not subclassable.
Guido van Rossum4acc25b2000-02-02 15:10:15 +000025- 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"""
Guido van Rossum85d89451994-06-23 11:53:27 +000031
Fred Drakee0a7f4f2000-09-28 04:21:06 +000032import errno
Guido van Rossum85d89451994-06-23 11:53:27 +000033import string
34
35class StringIO:
36 def __init__(self, buf = ''):
37 self.buf = buf
Guido van Rossumd3901021996-06-19 14:54:19 +000038 self.len = len(buf)
39 self.buflist = []
Guido van Rossum85d89451994-06-23 11:53:27 +000040 self.pos = 0
41 self.closed = 0
Guido van Rossum0daa13b1995-06-22 18:45:04 +000042 self.softspace = 0
Guido van Rossum85d89451994-06-23 11:53:27 +000043 def close(self):
44 if not self.closed:
45 self.closed = 1
46 del self.buf, self.pos
47 def isatty(self):
Fred Drakece4ba891998-08-18 17:43:08 +000048 if self.closed:
49 raise ValueError, "I/O operation on closed file"
Guido van Rossum85d89451994-06-23 11:53:27 +000050 return 0
51 def seek(self, pos, mode = 0):
Fred Drakece4ba891998-08-18 17:43:08 +000052 if self.closed:
53 raise ValueError, "I/O operation on closed file"
Guido van Rossumd3901021996-06-19 14:54:19 +000054 if self.buflist:
55 self.buf = self.buf + string.joinfields(self.buflist, '')
56 self.buflist = []
Guido van Rossum85d89451994-06-23 11:53:27 +000057 if mode == 1:
58 pos = pos + self.pos
59 elif mode == 2:
Guido van Rossumd3901021996-06-19 14:54:19 +000060 pos = pos + self.len
Guido van Rossum85d89451994-06-23 11:53:27 +000061 self.pos = max(0, pos)
62 def tell(self):
Fred Drakece4ba891998-08-18 17:43:08 +000063 if self.closed:
64 raise ValueError, "I/O operation on closed file"
Guido van Rossum85d89451994-06-23 11:53:27 +000065 return self.pos
Guido van Rossumf7476c51996-01-25 17:34:14 +000066 def read(self, n = -1):
Fred Drakece4ba891998-08-18 17:43:08 +000067 if self.closed:
68 raise ValueError, "I/O operation on closed file"
Guido van Rossumd3901021996-06-19 14:54:19 +000069 if self.buflist:
70 self.buf = self.buf + string.joinfields(self.buflist, '')
71 self.buflist = []
Guido van Rossumf7476c51996-01-25 17:34:14 +000072 if n < 0:
Guido van Rossumd3901021996-06-19 14:54:19 +000073 newpos = self.len
Guido van Rossum85d89451994-06-23 11:53:27 +000074 else:
Guido van Rossumd3901021996-06-19 14:54:19 +000075 newpos = min(self.pos+n, self.len)
Guido van Rossum85d89451994-06-23 11:53:27 +000076 r = self.buf[self.pos:newpos]
77 self.pos = newpos
78 return r
Guido van Rossum2e2525f1997-07-25 14:56:01 +000079 def readline(self, length=None):
Fred Drakece4ba891998-08-18 17:43:08 +000080 if self.closed:
81 raise ValueError, "I/O operation on closed file"
Guido van Rossumd3901021996-06-19 14:54:19 +000082 if self.buflist:
83 self.buf = self.buf + string.joinfields(self.buflist, '')
84 self.buflist = []
Guido van Rossum85d89451994-06-23 11:53:27 +000085 i = string.find(self.buf, '\n', self.pos)
86 if i < 0:
Guido van Rossumd3901021996-06-19 14:54:19 +000087 newpos = self.len
Guido van Rossum85d89451994-06-23 11:53:27 +000088 else:
89 newpos = i+1
Guido van Rossum2e2525f1997-07-25 14:56:01 +000090 if length is not None:
91 if self.pos + length < newpos:
92 newpos = self.pos + length
Guido van Rossum85d89451994-06-23 11:53:27 +000093 r = self.buf[self.pos:newpos]
94 self.pos = newpos
95 return r
Martin v. Löwisa05fa1d2000-09-19 11:07:44 +000096 def readlines(self, sizehint = 0):
97 total = 0
Guido van Rossum85d89451994-06-23 11:53:27 +000098 lines = []
99 line = self.readline()
100 while line:
101 lines.append(line)
Martin v. Löwisa05fa1d2000-09-19 11:07:44 +0000102 total += len(line)
103 if 0 < sizehint <= total:
104 break
Guido van Rossum85d89451994-06-23 11:53:27 +0000105 line = self.readline()
106 return lines
Fred Drakee0a7f4f2000-09-28 04:21:06 +0000107 def truncate(self, size=None):
108 if self.closed:
109 raise ValueError, "I/O operation on closed file"
110 if size is None:
111 size = self.pos
112 elif size < 0:
113 raise IOError(errno.EINVAL,
114 "Negative size not allowed")
115 elif size < self.pos:
116 self.pos = size
117 self.buf = self.getvalue()[:size]
Guido van Rossum85d89451994-06-23 11:53:27 +0000118 def write(self, s):
Fred Drakece4ba891998-08-18 17:43:08 +0000119 if self.closed:
120 raise ValueError, "I/O operation on closed file"
Guido van Rossum85d89451994-06-23 11:53:27 +0000121 if not s: return
Guido van Rossumd3901021996-06-19 14:54:19 +0000122 if self.pos > self.len:
123 self.buflist.append('\0'*(self.pos - self.len))
124 self.len = self.pos
Guido van Rossum85d89451994-06-23 11:53:27 +0000125 newpos = self.pos + len(s)
Guido van Rossumd3901021996-06-19 14:54:19 +0000126 if self.pos < self.len:
127 if self.buflist:
128 self.buf = self.buf + string.joinfields(self.buflist, '')
129 self.buflist = []
130 self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]]
131 self.buf = ''
Guido van Rossumb636dc62000-10-12 16:45:37 +0000132 if newpos > self.len:
133 self.len = newpos
Guido van Rossumd3901021996-06-19 14:54:19 +0000134 else:
135 self.buflist.append(s)
136 self.len = newpos
Guido van Rossum85d89451994-06-23 11:53:27 +0000137 self.pos = newpos
138 def writelines(self, list):
139 self.write(string.joinfields(list, ''))
Sjoerd Mullenderaa3e1631995-07-19 11:21:21 +0000140 def flush(self):
Fred Drakece4ba891998-08-18 17:43:08 +0000141 if self.closed:
142 raise ValueError, "I/O operation on closed file"
Guido van Rossum85d89451994-06-23 11:53:27 +0000143 def getvalue(self):
Guido van Rossumd3901021996-06-19 14:54:19 +0000144 if self.buflist:
145 self.buf = self.buf + string.joinfields(self.buflist, '')
146 self.buflist = []
Guido van Rossum85d89451994-06-23 11:53:27 +0000147 return self.buf
148
149
150# A little test suite
151
152def test():
153 import sys
154 if sys.argv[1:]:
155 file = sys.argv[1]
156 else:
157 file = '/etc/passwd'
158 lines = open(file, 'r').readlines()
159 text = open(file, 'r').read()
160 f = StringIO()
161 for line in lines[:-2]:
162 f.write(line)
163 f.writelines(lines[-2:])
164 if f.getvalue() != text:
165 raise RuntimeError, 'write failed'
166 length = f.tell()
167 print 'File length =', length
168 f.seek(len(lines[0]))
169 f.write(lines[1])
170 f.seek(0)
171 print 'First line =', `f.readline()`
172 here = f.tell()
173 line = f.readline()
174 print 'Second line =', `line`
175 f.seek(-len(line), 1)
176 line2 = f.read(len(line))
177 if line != line2:
178 raise RuntimeError, 'bad result after seek back'
179 f.seek(len(line2), 1)
180 list = f.readlines()
181 line = list[-1]
182 f.seek(f.tell() - len(line))
183 line2 = f.read()
184 if line != line2:
185 raise RuntimeError, 'bad result after seek back from EOF'
186 print 'Read', len(list), 'more lines'
187 print 'File length =', f.tell()
188 if f.tell() != length:
189 raise RuntimeError, 'bad length'
190 f.close()
191
192if __name__ == '__main__':
193 test()