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
|
# class StringIO implements file-like objects that read/write a
# string buffer (a.k.a. "memory files").
#
# 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.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).
# - 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 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):
return 0
def seek(self, pos, mode = 0):
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):
return self.pos
def read(self, n = -1):
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):
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
r = self.buf[self.pos:newpos]
self.pos = newpos
return r
def readlines(self):
lines = []
line = self.readline()
while line:
lines.append(line)
line = self.readline()
return lines
def write(self, s):
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):
pass
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()
|
