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
|
"""File-like objects that read/write an array buffer.
This implements (nearly) all stdio methods.
f = ArrayIO() # ready for writing
f = ArrayIO(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:
- This is very similar to StringIO. StringIO is faster for reading,
but ArrayIO is faster for writing.
- ArrayIO uses an array object internally, but all its interfaces
accept and return strings.
- 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
from array import array
class ArrayIO:
def __init__(self, buf = ''):
self.buf = array('c', buf)
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 mode == 1:
pos = pos + self.pos
elif mode == 2:
pos = pos + len(self.buf)
self.pos = max(0, pos)
def tell(self):
return self.pos
def read(self, n = -1):
if n < 0:
newpos = len(self.buf)
else:
newpos = min(self.pos+n, len(self.buf))
r = self.buf[self.pos:newpos].tostring()
self.pos = newpos
return r
def readline(self):
i = string.find(self.buf[self.pos:].tostring(), '\n')
if i < 0:
newpos = len(self.buf)
else:
newpos = self.pos+i+1
r = self.buf[self.pos:newpos].tostring()
self.pos = newpos
return r
def readlines(self):
lines = string.splitfields(self.read(), '\n')
if not lines:
return lines
for i in range(len(lines)-1):
lines[i] = lines[i] + '\n'
if not lines[-1]:
del lines[-1]
return lines
def write(self, s):
if not s: return
a = array('c', s)
n = self.pos - len(self.buf)
if n > 0:
self.buf[len(self.buf):] = array('c', '\0')*n
newpos = self.pos + len(a)
self.buf[self.pos:newpos] = a
self.pos = newpos
def writelines(self, list):
self.write(string.joinfields(list, ''))
def flush(self):
pass
def getvalue(self):
return self.buf.tostring()
# 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 = ArrayIO()
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()
|
