"""Conversion pipeline templates.
Suppose you have some data that you want to convert to another format,
such as from GIF image format to PPM image format. Maybe the
conversion involves several steps (e.g. piping it through compress or
uuencode). Some of the conversion steps may require that their input
is a disk file, others may be able to read standard input; similar for
their output. The input to the entire conversion may also be read
from a disk file or from an open file, and similar for its output.
The module lets you construct a pipeline template by sticking one or
more conversion steps together. It will take care of creating and
removing temporary files if they are necessary to hold intermediate
data. You can then use the template to do conversions from many
different sources to many different destinations. The temporary
file names used are different each time the template is used.
The templates are objects so you can create templates for many
different conversion steps and store them in a dictionary, for
To add a conversion step to a template:
where kind is a string of two characters: the first is '-' if the
command reads its standard input or 'f' if it requires a file; the
second likewise for the output. The command must be valid /bin/sh
syntax. If input or output files are required, they are passed as
$IN and $OUT; otherwise, it must be possible to use the command in
To add a conversion step at the beginning:
To convert a file to another file using a template:
sts = t.copy(infile, outfile)
If infile or outfile are the empty string, standard input is read or
standard output is written, respectively. The return value is the
exit status of the conversion pipeline.
To open a file for reading or writing through a conversion pipeline:
where mode is 'r' to read the file, or 'w' to write it -- just like
for the built-in function open() or for os.popen().
To create a new template object initialized to a given one:
# we import the quote function rather than the module for backward compat
# (quote used to be an undocumented but used function in pipes)
FILEIN_FILEOUT = 'ff' # Must read & write real files
STDIN_FILEOUT = '-f' # Must write a real file
FILEIN_STDOUT = 'f-' # Must read a real file
STDIN_STDOUT = '--' # Normal pipeline element
SOURCE = '.-' # Must be first, writes stdout
SINK = '-.' # Must be last, reads stdin
stepkinds = [FILEIN_FILEOUT, STDIN_FILEOUT, FILEIN_STDOUT, STDIN_STDOUT, \
"""Class representing a pipeline template."""
"""Template() returns a fresh pipeline template."""
"""t.__repr__() implements repr(t)."""
return '<Template instance, steps=%r>' % (self.steps,)
"""t.reset() restores a pipeline template to its initial state."""
"""t.clone() returns a new pipeline template with identical
initial state as the current one."""
t.debugging = self.debugging
"""t.debug(flag) turns debugging on or off."""
def append(self, cmd, kind):
"""t.append(cmd, kind) adds a new step at the end."""
if type(cmd) is not type(''):
raise TypeError('Template.append: cmd must be a string')
if kind not in stepkinds:
raise ValueError('Template.append: bad kind %r' % (kind,))
raise ValueError('Template.append: SOURCE can only be prepended')
if self.steps and self.steps[-1][1] == SINK:
raise ValueError('Template.append: already ends with SINK')
if kind[0] == 'f' and not re.search(r'\$IN\b', cmd):
raise ValueError('Template.append: missing $IN in cmd')
if kind[1] == 'f' and not re.search(r'\$OUT\b', cmd):
raise ValueError('Template.append: missing $OUT in cmd')
self.steps.append((cmd, kind))
def prepend(self, cmd, kind):
"""t.prepend(cmd, kind) adds a new step at the front."""
if type(cmd) is not type(''):
raise TypeError('Template.prepend: cmd must be a string')
if kind not in stepkinds:
raise ValueError('Template.prepend: bad kind %r' % (kind,))
raise ValueError('Template.prepend: SINK can only be appended')
if self.steps and self.steps[0][1] == SOURCE:
raise ValueError('Template.prepend: already begins with SOURCE')
if kind[0] == 'f' and not re.search(r'\$IN\b', cmd):
raise ValueError('Template.prepend: missing $IN in cmd')
if kind[1] == 'f' and not re.search(r'\$OUT\b', cmd):
raise ValueError('Template.prepend: missing $OUT in cmd')
self.steps.insert(0, (cmd, kind))
def open(self, file, rw):
"""t.open(file, rw) returns a pipe or file object open for
reading or writing; the file is the other end of the pipeline."""
raise ValueError('Template.open: rw must be \'r\' or \'w\', not %r'
"""t.open_r(file) and t.open_w(file) implement
t.open(file, 'r') and t.open(file, 'w') respectively."""
if self.steps[-1][1] == SINK:
raise ValueError('Template.open_r: pipeline ends width SINK')
cmd = self.makepipeline(file, '')
return os.popen(cmd, 'r')
if self.steps[0][1] == SOURCE:
raise ValueError('Template.open_w: pipeline begins with SOURCE')
cmd = self.makepipeline('', file)
return os.popen(cmd, 'w')
def copy(self, infile, outfile):
return os.system(self.makepipeline(infile, outfile))
def makepipeline(self, infile, outfile):
cmd = makepipeline(infile, self.steps, outfile)
def makepipeline(infile, steps, outfile):
# Build a list with for each command:
# [input filename or '', command string, kind, output filename or '']
list.append(['', cmd, kind, ''])
# Make sure there is at least one step
list.append(['', 'cat', '--', ''])
# Take care of the input and output ends
[cmd, kind] = list[0][1:3]
if kind[0] == 'f' and not infile:
list.insert(0, ['', 'cat', '--', ''])
[cmd, kind] = list[-1][1:3]
if kind[1] == 'f' and not outfile:
list.append(['', 'cat', '--', ''])
# Invent temporary files to connect stages that need files
for i in range(1, len(list)):
if lkind[1] == 'f' or rkind[0] == 'f':
(fd, temp) = tempfile.mkstemp()
list[i-1][-1] = list[i][0] = temp
[inf, cmd, kind, outf] = item
cmd = 'OUT=' + quote(outf) + '; ' + cmd
cmd = 'IN=' + quote(inf) + '; ' + cmd
if kind[0] == '-' and inf:
cmd = cmd + ' <' + quote(inf)
if kind[1] == '-' and outf:
cmd = cmd + ' >' + quote(outf)
cmdlist = cmdlist + ' |\n' + cmd
cmdlist = cmdlist + '\n' + cmd
rmcmd = rmcmd + ' ' + quote(file)
trapcmd = 'trap ' + quote(rmcmd + '; exit') + ' 1 2 3 13 14 15'
cmdlist = trapcmd + '\n' + cmdlist + '\n' + rmcmd
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