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Guido van Rossum85d89451994-06-23 11:53:27 +00001# class StringIO implements file-like objects that read/write a
2# string buffer (a.k.a. "memory files").
3#
4# This implements (nearly) all stdio methods.
5#
6# f = StringIO() # ready for writing
7# f = StringIO(buf) # ready for reading
8# f.close() # explicitly release resources held
9# flag = f.isatty() # always false
10# pos = f.tell() # get current position
11# f.seek(pos) # set current position
12# f.seek(pos, mode) # mode 0: absolute; 1: relative; 2: relative to EOF
13# buf = f.read() # read until EOF
14# buf = f.read(n) # read up to n bytes
15# buf = f.readline() # read until end of line ('\n') or EOF
16# list = f.readlines()# list of f.readline() results until EOF
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# - fileno() is left unimplemented so that code which uses it triggers
24# an exception early.
25# - Seeking far beyond EOF and then writing will insert real null
26# bytes that occupy space in the buffer.
27# - There's a simple test set (see end of this file).
28
29import string
30
31class StringIO:
32 def __init__(self, buf = ''):
33 self.buf = buf
Guido van Rossumd3901021996-06-19 14:54:19 +000034 self.len = len(buf)
35 self.buflist = []
Guido van Rossum85d89451994-06-23 11:53:27 +000036 self.pos = 0
37 self.closed = 0
Guido van Rossum0daa13b1995-06-22 18:45:04 +000038 self.softspace = 0
Guido van Rossum85d89451994-06-23 11:53:27 +000039 def close(self):
40 if not self.closed:
41 self.closed = 1
42 del self.buf, self.pos
43 def isatty(self):
Fred Drakece4ba891998-08-18 17:43:08 +000044 if self.closed:
45 raise ValueError, "I/O operation on closed file"
Guido van Rossum85d89451994-06-23 11:53:27 +000046 return 0
47 def seek(self, pos, mode = 0):
Fred Drakece4ba891998-08-18 17:43:08 +000048 if self.closed:
49 raise ValueError, "I/O operation on closed file"
Guido van Rossumd3901021996-06-19 14:54:19 +000050 if self.buflist:
51 self.buf = self.buf + string.joinfields(self.buflist, '')
52 self.buflist = []
Guido van Rossum85d89451994-06-23 11:53:27 +000053 if mode == 1:
54 pos = pos + self.pos
55 elif mode == 2:
Guido van Rossumd3901021996-06-19 14:54:19 +000056 pos = pos + self.len
Guido van Rossum85d89451994-06-23 11:53:27 +000057 self.pos = max(0, pos)
58 def tell(self):
Fred Drakece4ba891998-08-18 17:43:08 +000059 if self.closed:
60 raise ValueError, "I/O operation on closed file"
Guido van Rossum85d89451994-06-23 11:53:27 +000061 return self.pos
Guido van Rossumf7476c51996-01-25 17:34:14 +000062 def read(self, n = -1):
Fred Drakece4ba891998-08-18 17:43:08 +000063 if self.closed:
64 raise ValueError, "I/O operation on closed file"
Guido van Rossumd3901021996-06-19 14:54:19 +000065 if self.buflist:
66 self.buf = self.buf + string.joinfields(self.buflist, '')
67 self.buflist = []
Guido van Rossumf7476c51996-01-25 17:34:14 +000068 if n < 0:
Guido van Rossumd3901021996-06-19 14:54:19 +000069 newpos = self.len
Guido van Rossum85d89451994-06-23 11:53:27 +000070 else:
Guido van Rossumd3901021996-06-19 14:54:19 +000071 newpos = min(self.pos+n, self.len)
Guido van Rossum85d89451994-06-23 11:53:27 +000072 r = self.buf[self.pos:newpos]
73 self.pos = newpos
74 return r
Guido van Rossum2e2525f1997-07-25 14:56:01 +000075 def readline(self, length=None):
Fred Drakece4ba891998-08-18 17:43:08 +000076 if self.closed:
77 raise ValueError, "I/O operation on closed file"
Guido van Rossumd3901021996-06-19 14:54:19 +000078 if self.buflist:
79 self.buf = self.buf + string.joinfields(self.buflist, '')
80 self.buflist = []
Guido van Rossum85d89451994-06-23 11:53:27 +000081 i = string.find(self.buf, '\n', self.pos)
82 if i < 0:
Guido van Rossumd3901021996-06-19 14:54:19 +000083 newpos = self.len
Guido van Rossum85d89451994-06-23 11:53:27 +000084 else:
85 newpos = i+1
Guido van Rossum2e2525f1997-07-25 14:56:01 +000086 if length is not None:
87 if self.pos + length < newpos:
88 newpos = self.pos + length
Guido van Rossum85d89451994-06-23 11:53:27 +000089 r = self.buf[self.pos:newpos]
90 self.pos = newpos
91 return r
92 def readlines(self):
93 lines = []
94 line = self.readline()
95 while line:
96 lines.append(line)
97 line = self.readline()
98 return lines
99 def write(self, s):
Fred Drakece4ba891998-08-18 17:43:08 +0000100 if self.closed:
101 raise ValueError, "I/O operation on closed file"
Guido van Rossum85d89451994-06-23 11:53:27 +0000102 if not s: return
Guido van Rossumd3901021996-06-19 14:54:19 +0000103 if self.pos > self.len:
104 self.buflist.append('\0'*(self.pos - self.len))
105 self.len = self.pos
Guido van Rossum85d89451994-06-23 11:53:27 +0000106 newpos = self.pos + len(s)
Guido van Rossumd3901021996-06-19 14:54:19 +0000107 if self.pos < self.len:
108 if self.buflist:
109 self.buf = self.buf + string.joinfields(self.buflist, '')
110 self.buflist = []
111 self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]]
112 self.buf = ''
113 else:
114 self.buflist.append(s)
115 self.len = newpos
Guido van Rossum85d89451994-06-23 11:53:27 +0000116 self.pos = newpos
117 def writelines(self, list):
118 self.write(string.joinfields(list, ''))
Sjoerd Mullenderaa3e1631995-07-19 11:21:21 +0000119 def flush(self):
Fred Drakece4ba891998-08-18 17:43:08 +0000120 if self.closed:
121 raise ValueError, "I/O operation on closed file"
Guido van Rossum85d89451994-06-23 11:53:27 +0000122 def getvalue(self):
Guido van Rossumd3901021996-06-19 14:54:19 +0000123 if self.buflist:
124 self.buf = self.buf + string.joinfields(self.buflist, '')
125 self.buflist = []
Guido van Rossum85d89451994-06-23 11:53:27 +0000126 return self.buf
127
128
129# A little test suite
130
131def test():
132 import sys
133 if sys.argv[1:]:
134 file = sys.argv[1]
135 else:
136 file = '/etc/passwd'
137 lines = open(file, 'r').readlines()
138 text = open(file, 'r').read()
139 f = StringIO()
140 for line in lines[:-2]:
141 f.write(line)
142 f.writelines(lines[-2:])
143 if f.getvalue() != text:
144 raise RuntimeError, 'write failed'
145 length = f.tell()
146 print 'File length =', length
147 f.seek(len(lines[0]))
148 f.write(lines[1])
149 f.seek(0)
150 print 'First line =', `f.readline()`
151 here = f.tell()
152 line = f.readline()
153 print 'Second line =', `line`
154 f.seek(-len(line), 1)
155 line2 = f.read(len(line))
156 if line != line2:
157 raise RuntimeError, 'bad result after seek back'
158 f.seek(len(line2), 1)
159 list = f.readlines()
160 line = list[-1]
161 f.seek(f.tell() - len(line))
162 line2 = f.read()
163 if line != line2:
164 raise RuntimeError, 'bad result after seek back from EOF'
165 print 'Read', len(list), 'more lines'
166 print 'File length =', f.tell()
167 if f.tell() != length:
168 raise RuntimeError, 'bad length'
169 f.close()
170
171if __name__ == '__main__':
172 test()