Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 1 | # 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 | |
| 29 | import string |
| 30 | |
| 31 | class StringIO: |
| 32 | def __init__(self, buf = ''): |
| 33 | self.buf = buf |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 34 | self.len = len(buf) |
| 35 | self.buflist = [] |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 36 | self.pos = 0 |
| 37 | self.closed = 0 |
Guido van Rossum | 0daa13b | 1995-06-22 18:45:04 +0000 | [diff] [blame] | 38 | self.softspace = 0 |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 39 | def close(self): |
| 40 | if not self.closed: |
| 41 | self.closed = 1 |
| 42 | del self.buf, self.pos |
| 43 | def isatty(self): |
| 44 | return 0 |
| 45 | def seek(self, pos, mode = 0): |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 46 | if self.buflist: |
| 47 | self.buf = self.buf + string.joinfields(self.buflist, '') |
| 48 | self.buflist = [] |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 49 | if mode == 1: |
| 50 | pos = pos + self.pos |
| 51 | elif mode == 2: |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 52 | pos = pos + self.len |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 53 | self.pos = max(0, pos) |
| 54 | def tell(self): |
| 55 | return self.pos |
Guido van Rossum | f7476c5 | 1996-01-25 17:34:14 +0000 | [diff] [blame] | 56 | def read(self, n = -1): |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 57 | if self.buflist: |
| 58 | self.buf = self.buf + string.joinfields(self.buflist, '') |
| 59 | self.buflist = [] |
Guido van Rossum | f7476c5 | 1996-01-25 17:34:14 +0000 | [diff] [blame] | 60 | if n < 0: |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 61 | newpos = self.len |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 62 | else: |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 63 | newpos = min(self.pos+n, self.len) |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 64 | r = self.buf[self.pos:newpos] |
| 65 | self.pos = newpos |
| 66 | return r |
Guido van Rossum | 2e2525f | 1997-07-25 14:56:01 +0000 | [diff] [blame] | 67 | def readline(self, length=None): |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 68 | if self.buflist: |
| 69 | self.buf = self.buf + string.joinfields(self.buflist, '') |
| 70 | self.buflist = [] |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 71 | i = string.find(self.buf, '\n', self.pos) |
| 72 | if i < 0: |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 73 | newpos = self.len |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 74 | else: |
| 75 | newpos = i+1 |
Guido van Rossum | 2e2525f | 1997-07-25 14:56:01 +0000 | [diff] [blame] | 76 | if length is not None: |
| 77 | if self.pos + length < newpos: |
| 78 | newpos = self.pos + length |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 79 | r = self.buf[self.pos:newpos] |
| 80 | self.pos = newpos |
| 81 | return r |
| 82 | def readlines(self): |
| 83 | lines = [] |
| 84 | line = self.readline() |
| 85 | while line: |
| 86 | lines.append(line) |
| 87 | line = self.readline() |
| 88 | return lines |
| 89 | def write(self, s): |
| 90 | if not s: return |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 91 | if self.pos > self.len: |
| 92 | self.buflist.append('\0'*(self.pos - self.len)) |
| 93 | self.len = self.pos |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 94 | newpos = self.pos + len(s) |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 95 | if self.pos < self.len: |
| 96 | if self.buflist: |
| 97 | self.buf = self.buf + string.joinfields(self.buflist, '') |
| 98 | self.buflist = [] |
| 99 | self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]] |
| 100 | self.buf = '' |
| 101 | else: |
| 102 | self.buflist.append(s) |
| 103 | self.len = newpos |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 104 | self.pos = newpos |
| 105 | def writelines(self, list): |
| 106 | self.write(string.joinfields(list, '')) |
Sjoerd Mullender | aa3e163 | 1995-07-19 11:21:21 +0000 | [diff] [blame] | 107 | def flush(self): |
| 108 | pass |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 109 | def getvalue(self): |
Guido van Rossum | d390102 | 1996-06-19 14:54:19 +0000 | [diff] [blame] | 110 | if self.buflist: |
| 111 | self.buf = self.buf + string.joinfields(self.buflist, '') |
| 112 | self.buflist = [] |
Guido van Rossum | 85d8945 | 1994-06-23 11:53:27 +0000 | [diff] [blame] | 113 | return self.buf |
| 114 | |
| 115 | |
| 116 | # A little test suite |
| 117 | |
| 118 | def test(): |
| 119 | import sys |
| 120 | if sys.argv[1:]: |
| 121 | file = sys.argv[1] |
| 122 | else: |
| 123 | file = '/etc/passwd' |
| 124 | lines = open(file, 'r').readlines() |
| 125 | text = open(file, 'r').read() |
| 126 | f = StringIO() |
| 127 | for line in lines[:-2]: |
| 128 | f.write(line) |
| 129 | f.writelines(lines[-2:]) |
| 130 | if f.getvalue() != text: |
| 131 | raise RuntimeError, 'write failed' |
| 132 | length = f.tell() |
| 133 | print 'File length =', length |
| 134 | f.seek(len(lines[0])) |
| 135 | f.write(lines[1]) |
| 136 | f.seek(0) |
| 137 | print 'First line =', `f.readline()` |
| 138 | here = f.tell() |
| 139 | line = f.readline() |
| 140 | print 'Second line =', `line` |
| 141 | f.seek(-len(line), 1) |
| 142 | line2 = f.read(len(line)) |
| 143 | if line != line2: |
| 144 | raise RuntimeError, 'bad result after seek back' |
| 145 | f.seek(len(line2), 1) |
| 146 | list = f.readlines() |
| 147 | line = list[-1] |
| 148 | f.seek(f.tell() - len(line)) |
| 149 | line2 = f.read() |
| 150 | if line != line2: |
| 151 | raise RuntimeError, 'bad result after seek back from EOF' |
| 152 | print 'Read', len(list), 'more lines' |
| 153 | print 'File length =', f.tell() |
| 154 | if f.tell() != length: |
| 155 | raise RuntimeError, 'bad length' |
| 156 | f.close() |
| 157 | |
| 158 | if __name__ == '__main__': |
| 159 | test() |