1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
|
"""File-like objects that read from or write to a string buffer.
This implements (nearly) all stdio methods.
f = StringIO() # ready for writing
f = StringIO(buf) # ready for reading
f.close() # explicitly release resources held
flag = f.isatty() # always false
pos = f.tell() # get current position
f.seek(pos) # set current position
f.seek(pos, mode) # mode 0: absolute; 1: relative; 2: relative to EOF
buf = f.read() # read until EOF
buf = f.read(n) # read up to n bytes
buf = f.readline() # read until end of line ('\n') or EOF
list = f.readlines()# list of f.readline() results until EOF
f.truncate([size]) # truncate file at to at most size (default: current pos)
f.write(buf) # write at current position
f.writelines(list) # for line in list: f.write(line)
f.getvalue() # return whole file's contents as a string
Notes:
- Using a real file is often faster (but less convenient).
- There's also a much faster implementation in C, called cStringIO, but
it's not subclassable.
- fileno() is left unimplemented so that code which uses it triggers
an exception early.
- Seeking far beyond EOF and then writing will insert real null
bytes that occupy space in the buffer.
- There's a simple test set (see end of this file).
"""
import errno
import string
class StringIO:
def __init__(self, buf = ''):
self.buf = buf
self.len = len(buf)
self.buflist = []
self.pos = 0
self.closed = 0
self.softspace = 0
def close(self):
if not self.closed:
self.closed = 1
del self.buf, self.pos
def isatty(self):
if self.closed:
raise ValueError, "I/O operation on closed file"
return 0
def seek(self, pos, mode = 0):
if self.closed:
raise ValueError, "I/O operation on closed file"
if self.buflist:
self.buf = self.buf + string.joinfields(self.buflist, '')
self.buflist = []
if mode == 1:
pos = pos + self.pos
elif mode == 2:
pos = pos + self.len
self.pos = max(0, pos)
def tell(self):
if self.closed:
raise ValueError, "I/O operation on closed file"
return self.pos
def read(self, n = -1):
if self.closed:
raise ValueError, "I/O operation on closed file"
if self.buflist:
self.buf = self.buf + string.joinfields(self.buflist, '')
self.buflist = []
if n < 0:
newpos = self.len
else:
newpos = min(self.pos+n, self.len)
r = self.buf[self.pos:newpos]
self.pos = newpos
return r
def readline(self, length=None):
if self.closed:
raise ValueError, "I/O operation on closed file"
if self.buflist:
self.buf = self.buf + string.joinfields(self.buflist, '')
self.buflist = []
i = string.find(self.buf, '\n', self.pos)
if i < 0:
newpos = self.len
else:
newpos = i+1
if length is not None:
if self.pos + length < newpos:
newpos = self.pos + length
r = self.buf[self.pos:newpos]
self.pos = newpos
return r
def readlines(self, sizehint = 0):
total = 0
lines = []
line = self.readline()
while line:
lines.append(line)
total += len(line)
if 0 < sizehint <= total:
break
line = self.readline()
return lines
def truncate(self, size=None):
if self.closed:
raise ValueError, "I/O operation on closed file"
if size is None:
size = self.pos
elif size < 0:
raise IOError(errno.EINVAL,
"Negative size not allowed")
elif size < self.pos:
self.pos = size
self.buf = self.getvalue()[:size]
def write(self, s):
if self.closed:
raise ValueError, "I/O operation on closed file"
if not s: return
if self.pos > self.len:
self.buflist.append('\0'*(self.pos - self.len))
self.len = self.pos
newpos = self.pos + len(s)
if self.pos < self.len:
if self.buflist:
self.buf = self.buf + string.joinfields(self.buflist, '')
self.buflist = []
self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]]
self.buf = ''
else:
self.buflist.append(s)
self.len = newpos
self.pos = newpos
def writelines(self, list):
self.write(string.joinfields(list, ''))
def flush(self):
if self.closed:
raise ValueError, "I/O operation on closed file"
def getvalue(self):
if self.buflist:
self.buf = self.buf + string.joinfields(self.buflist, '')
self.buflist = []
return self.buf
# A little test suite
def test():
import sys
if sys.argv[1:]:
file = sys.argv[1]
else:
file = '/etc/passwd'
lines = open(file, 'r').readlines()
text = open(file, 'r').read()
f = StringIO()
for line in lines[:-2]:
f.write(line)
f.writelines(lines[-2:])
if f.getvalue() != text:
raise RuntimeError, 'write failed'
length = f.tell()
print 'File length =', length
f.seek(len(lines[0]))
f.write(lines[1])
f.seek(0)
print 'First line =', `f.readline()`
here = f.tell()
line = f.readline()
print 'Second line =', `line`
f.seek(-len(line), 1)
line2 = f.read(len(line))
if line != line2:
raise RuntimeError, 'bad result after seek back'
f.seek(len(line2), 1)
list = f.readlines()
line = list[-1]
f.seek(f.tell() - len(line))
line2 = f.read()
if line != line2:
raise RuntimeError, 'bad result after seek back from EOF'
print 'Read', len(list), 'more lines'
print 'File length =', f.tell()
if f.tell() != length:
raise RuntimeError, 'bad length'
f.close()
if __name__ == '__main__':
test()
|
