pipes

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diff --git a/modules/language/python/module/pipes.py b/modules/language/python/module/pipes.py
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+module(pipes)
+"""Conversion pipeline templates.
+
+The problem:
+------------
+
+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
+instance.
+
+
+Directions:
+-----------
+
+To create a template:
+    t = Template()
+
+To add a conversion step to a template:
+   t.append(command, kind)
+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
+a pipeline.
+
+To add a conversion step at the beginning:
+   t.prepend(command, kind)
+
+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:
+   fp = t.open(file, mode)
+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:
+   t2 = t.clone()
+"""                                     # '
+
+
+import re
+import os
+import tempfile
+# we import the quote function rather than the module for backward compat
+# (quote used to be an undocumented but used function in pipes)
+from shlex import quote
+
+__all__ = ["Template"]
+
+# Conversion step kinds
+
+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, \
+             SOURCE, SINK]
+
+
+class Template:
+    """Class representing a pipeline template."""
+
+    def __init__(self):
+        """Template() returns a fresh pipeline template."""
+        self.debugging = 0
+        self.reset()
+
+    def __repr__(self):
+        """t.__repr__() implements repr(t)."""
+        return '<Template instance, steps=%r>' % (self.steps,)
+
+    def reset(self):
+        """t.reset() restores a pipeline template to its initial state."""
+        self.steps = []
+
+    def clone(self):
+        """t.clone() returns a new pipeline template with identical
+        initial state as the current one."""
+        t = Template()
+        t.steps = self.steps[:]
+        t.debugging = self.debugging
+        return t
+
+    def debug(self, flag):
+        """t.debug(flag) turns debugging on or off."""
+        self.debugging = flag
+
+    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,))
+        if kind == SOURCE:
+            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,))
+        if kind == SINK:
+            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."""
+        if rw == 'r':
+            return self.open_r(file)
+        if rw == 'w':
+            return self.open_w(file)
+        raise ValueError('Template.open: rw must be \'r\' or \'w\', not %r'
+                         % (rw,))
+
+    def open_r(self, file):
+        """t.open_r(file) and t.open_w(file) implement
+        t.open(file, 'r') and t.open(file, 'w') respectively."""
+        if not self.steps:
+            return open(file, 'r')
+        if self.steps[-1][1] == SINK:
+            raise ValueError('Template.open_r: pipeline ends width SINK')
+        cmd = self.makepipeline(file, '')
+        return os.popen(cmd, 'r')
+
+    def open_w(self, file):
+        if not self.steps:
+            return open(file, 'w')
+        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)
+        if self.debugging:
+            print(cmd)
+            cmd = 'set -x; ' + cmd
+        return cmd
+
+
+def makepipeline(infile, steps, outfile):
+    # Build a list with for each command:
+    # [input filename or '', command string, kind, output filename or '']
+
+    list = []
+    for cmd, kind in steps:
+        list.append(['', cmd, kind, ''])
+    #
+    # Make sure there is at least one step
+    #
+    if not list:
+        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', '--', ''])
+    list[0][0] = infile
+    #
+    [cmd, kind] = list[-1][1:3]
+    if kind[1] == 'f' and not outfile:
+        list.append(['', 'cat', '--', ''])
+    list[-1][-1] = outfile
+    #
+    # Invent temporary files to connect stages that need files
+    #
+    garbage = []
+    for i in range(1, len(list)):
+        lkind = list[i-1][2]
+        rkind = list[i][2]
+        if lkind[1] == 'f' or rkind[0] == 'f':
+            (fd, temp) = tempfile.mkstemp()
+            os.close(fd)
+            garbage.append(temp)
+            list[i-1][-1] = list[i][0] = temp
+    #
+    for item in list:
+        [inf, cmd, kind, outf] = item
+        if kind[1] == 'f':
+            cmd = 'OUT=' + quote(outf) + '; ' + cmd
+        if kind[0] == 'f':
+            cmd = 'IN=' + quote(inf) + '; ' + cmd
+        if kind[0] == '-' and inf:
+            cmd = cmd + ' <' + quote(inf)
+        if kind[1] == '-' and outf:
+            cmd = cmd + ' >' + quote(outf)
+        item[1] = cmd
+    #
+    cmdlist = list[0][1]
+    for item in list[1:]:
+        [cmd, kind] = item[1:3]
+        if item[0] == '':
+            if 'f' in kind:
+                cmd = '{ ' + cmd + '; }'
+            cmdlist = cmdlist + ' |\n' + cmd
+        else:
+            cmdlist = cmdlist + '\n' + cmd
+    #
+    if garbage:
+        rmcmd = 'rm -f'
+        for file in garbage:
+            rmcmd = rmcmd + ' ' + quote(file)
+        trapcmd = 'trap ' + quote(rmcmd + '; exit') + ' 1 2 3 13 14 15'
+        cmdlist = trapcmd + '\n' + cmdlist + '\n' + rmcmd
+    #
+    return cmdlist