Add missing issue number in Misc/NEWS entry.
[python.git] / Lib / pipes.py
blob6dcc997b4c7327471116aa56a186ebdd482c8c16
1 """Conversion pipeline templates.
3 The problem:
4 ------------
6 Suppose you have some data that you want to convert to another format,
7 such as from GIF image format to PPM image format. Maybe the
8 conversion involves several steps (e.g. piping it through compress or
9 uuencode). Some of the conversion steps may require that their input
10 is a disk file, others may be able to read standard input; similar for
11 their output. The input to the entire conversion may also be read
12 from a disk file or from an open file, and similar for its output.
14 The module lets you construct a pipeline template by sticking one or
15 more conversion steps together. It will take care of creating and
16 removing temporary files if they are necessary to hold intermediate
17 data. You can then use the template to do conversions from many
18 different sources to many different destinations. The temporary
19 file names used are different each time the template is used.
21 The templates are objects so you can create templates for many
22 different conversion steps and store them in a dictionary, for
23 instance.
26 Directions:
27 -----------
29 To create a template:
30 t = Template()
32 To add a conversion step to a template:
33 t.append(command, kind)
34 where kind is a string of two characters: the first is '-' if the
35 command reads its standard input or 'f' if it requires a file; the
36 second likewise for the output. The command must be valid /bin/sh
37 syntax. If input or output files are required, they are passed as
38 $IN and $OUT; otherwise, it must be possible to use the command in
39 a pipeline.
41 To add a conversion step at the beginning:
42 t.prepend(command, kind)
44 To convert a file to another file using a template:
45 sts = t.copy(infile, outfile)
46 If infile or outfile are the empty string, standard input is read or
47 standard output is written, respectively. The return value is the
48 exit status of the conversion pipeline.
50 To open a file for reading or writing through a conversion pipeline:
51 fp = t.open(file, mode)
52 where mode is 'r' to read the file, or 'w' to write it -- just like
53 for the built-in function open() or for os.popen().
55 To create a new template object initialized to a given one:
56 t2 = t.clone()
58 For an example, see the function test() at the end of the file.
59 """ # '
62 import re
63 import os
64 import tempfile
65 import string
67 __all__ = ["Template"]
69 # Conversion step kinds
71 FILEIN_FILEOUT = 'ff' # Must read & write real files
72 STDIN_FILEOUT = '-f' # Must write a real file
73 FILEIN_STDOUT = 'f-' # Must read a real file
74 STDIN_STDOUT = '--' # Normal pipeline element
75 SOURCE = '.-' # Must be first, writes stdout
76 SINK = '-.' # Must be last, reads stdin
78 stepkinds = [FILEIN_FILEOUT, STDIN_FILEOUT, FILEIN_STDOUT, STDIN_STDOUT, \
79 SOURCE, SINK]
82 class Template:
83 """Class representing a pipeline template."""
85 def __init__(self):
86 """Template() returns a fresh pipeline template."""
87 self.debugging = 0
88 self.reset()
90 def __repr__(self):
91 """t.__repr__() implements repr(t)."""
92 return '<Template instance, steps=%r>' % (self.steps,)
94 def reset(self):
95 """t.reset() restores a pipeline template to its initial state."""
96 self.steps = []
98 def clone(self):
99 """t.clone() returns a new pipeline template with identical
100 initial state as the current one."""
101 t = Template()
102 t.steps = self.steps[:]
103 t.debugging = self.debugging
104 return t
106 def debug(self, flag):
107 """t.debug(flag) turns debugging on or off."""
108 self.debugging = flag
110 def append(self, cmd, kind):
111 """t.append(cmd, kind) adds a new step at the end."""
112 if type(cmd) is not type(''):
113 raise TypeError, \
114 'Template.append: cmd must be a string'
115 if kind not in stepkinds:
116 raise ValueError, \
117 'Template.append: bad kind %r' % (kind,)
118 if kind == SOURCE:
119 raise ValueError, \
120 'Template.append: SOURCE can only be prepended'
121 if self.steps and self.steps[-1][1] == SINK:
122 raise ValueError, \
123 'Template.append: already ends with SINK'
124 if kind[0] == 'f' and not re.search(r'\$IN\b', cmd):
125 raise ValueError, \
126 'Template.append: missing $IN in cmd'
127 if kind[1] == 'f' and not re.search(r'\$OUT\b', cmd):
128 raise ValueError, \
129 'Template.append: missing $OUT in cmd'
130 self.steps.append((cmd, kind))
132 def prepend(self, cmd, kind):
133 """t.prepend(cmd, kind) adds a new step at the front."""
134 if type(cmd) is not type(''):
135 raise TypeError, \
136 'Template.prepend: cmd must be a string'
137 if kind not in stepkinds:
138 raise ValueError, \
139 'Template.prepend: bad kind %r' % (kind,)
140 if kind == SINK:
141 raise ValueError, \
142 'Template.prepend: SINK can only be appended'
143 if self.steps and self.steps[0][1] == SOURCE:
144 raise ValueError, \
145 'Template.prepend: already begins with SOURCE'
146 if kind[0] == 'f' and not re.search(r'\$IN\b', cmd):
147 raise ValueError, \
148 'Template.prepend: missing $IN in cmd'
149 if kind[1] == 'f' and not re.search(r'\$OUT\b', cmd):
150 raise ValueError, \
151 'Template.prepend: missing $OUT in cmd'
152 self.steps.insert(0, (cmd, kind))
154 def open(self, file, rw):
155 """t.open(file, rw) returns a pipe or file object open for
156 reading or writing; the file is the other end of the pipeline."""
157 if rw == 'r':
158 return self.open_r(file)
159 if rw == 'w':
160 return self.open_w(file)
161 raise ValueError, \
162 'Template.open: rw must be \'r\' or \'w\', not %r' % (rw,)
164 def open_r(self, file):
165 """t.open_r(file) and t.open_w(file) implement
166 t.open(file, 'r') and t.open(file, 'w') respectively."""
167 if not self.steps:
168 return open(file, 'r')
169 if self.steps[-1][1] == SINK:
170 raise ValueError, \
171 'Template.open_r: pipeline ends width SINK'
172 cmd = self.makepipeline(file, '')
173 return os.popen(cmd, 'r')
175 def open_w(self, file):
176 if not self.steps:
177 return open(file, 'w')
178 if self.steps[0][1] == SOURCE:
179 raise ValueError, \
180 'Template.open_w: pipeline begins with SOURCE'
181 cmd = self.makepipeline('', file)
182 return os.popen(cmd, 'w')
184 def copy(self, infile, outfile):
185 return os.system(self.makepipeline(infile, outfile))
187 def makepipeline(self, infile, outfile):
188 cmd = makepipeline(infile, self.steps, outfile)
189 if self.debugging:
190 print cmd
191 cmd = 'set -x; ' + cmd
192 return cmd
195 def makepipeline(infile, steps, outfile):
196 # Build a list with for each command:
197 # [input filename or '', command string, kind, output filename or '']
199 list = []
200 for cmd, kind in steps:
201 list.append(['', cmd, kind, ''])
203 # Make sure there is at least one step
205 if not list:
206 list.append(['', 'cat', '--', ''])
208 # Take care of the input and output ends
210 [cmd, kind] = list[0][1:3]
211 if kind[0] == 'f' and not infile:
212 list.insert(0, ['', 'cat', '--', ''])
213 list[0][0] = infile
215 [cmd, kind] = list[-1][1:3]
216 if kind[1] == 'f' and not outfile:
217 list.append(['', 'cat', '--', ''])
218 list[-1][-1] = outfile
220 # Invent temporary files to connect stages that need files
222 garbage = []
223 for i in range(1, len(list)):
224 lkind = list[i-1][2]
225 rkind = list[i][2]
226 if lkind[1] == 'f' or rkind[0] == 'f':
227 (fd, temp) = tempfile.mkstemp()
228 os.close(fd)
229 garbage.append(temp)
230 list[i-1][-1] = list[i][0] = temp
232 for item in list:
233 [inf, cmd, kind, outf] = item
234 if kind[1] == 'f':
235 cmd = 'OUT=' + quote(outf) + '; ' + cmd
236 if kind[0] == 'f':
237 cmd = 'IN=' + quote(inf) + '; ' + cmd
238 if kind[0] == '-' and inf:
239 cmd = cmd + ' <' + quote(inf)
240 if kind[1] == '-' and outf:
241 cmd = cmd + ' >' + quote(outf)
242 item[1] = cmd
244 cmdlist = list[0][1]
245 for item in list[1:]:
246 [cmd, kind] = item[1:3]
247 if item[0] == '':
248 if 'f' in kind:
249 cmd = '{ ' + cmd + '; }'
250 cmdlist = cmdlist + ' |\n' + cmd
251 else:
252 cmdlist = cmdlist + '\n' + cmd
254 if garbage:
255 rmcmd = 'rm -f'
256 for file in garbage:
257 rmcmd = rmcmd + ' ' + quote(file)
258 trapcmd = 'trap ' + quote(rmcmd + '; exit') + ' 1 2 3 13 14 15'
259 cmdlist = trapcmd + '\n' + cmdlist + '\n' + rmcmd
261 return cmdlist
264 # Reliably quote a string as a single argument for /bin/sh
266 _safechars = string.ascii_letters + string.digits + '!@%_-+=:,./' # Safe unquoted
267 _funnychars = '"`$\\' # Unsafe inside "double quotes"
269 def quote(file):
270 for c in file:
271 if c not in _safechars:
272 break
273 else:
274 return file
275 if '\'' not in file:
276 return '\'' + file + '\''
277 res = ''
278 for c in file:
279 if c in _funnychars:
280 c = '\\' + c
281 res = res + c
282 return '"' + res + '"'