cpython/Lib/pipes.py

301 lines
8.6 KiB
Python
Raw Normal View History

# Conversion pipeline templates
# =============================
# The problem:
# ------------
#
# Suppose you have some data that you want to convert to another format
# (e.g. 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()
#
# For an example, see the function test() at the end of the file.
import sys
import re
import os
import tempfile
import string
# 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]
# A pipeline template is a Template object:
class Template:
# Template() returns a fresh pipeline template
def __init__(self):
self.debugging = 0
self.reset()
# t.__repr__() implements `t`
def __repr__(self):
return '<Template instance, steps=' + `self.steps` + '>'
# t.reset() restores a pipeline template to its initial state
def reset(self):
self.steps = []
# t.clone() returns a new pipeline template with identical
# initial state as the current one
def clone(self):
t = Template()
t.steps = self.steps[:]
t.debugging = self.debugging
return t
# t.debug(flag) turns debugging on or off
def debug(self, flag):
self.debugging = flag
# t.append(cmd, kind) adds a new step at the end
def append(self, cmd, kind):
if type(cmd) <> type(''):
raise TypeError, \
'Template.append: cmd must be a string'
if kind not in stepkinds:
raise ValueError, \
'Template.append: bad kind ' + `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('\$IN\b', cmd):
raise ValueError, \
'Template.append: missing $IN in cmd'
if kind[1] == 'f' and not re.search('\$OUT\b', cmd):
raise ValueError, \
'Template.append: missing $OUT in cmd'
self.steps.append((cmd, kind))
# t.prepend(cmd, kind) adds a new step at the front
def prepend(self, cmd, kind):
if type(cmd) <> type(''):
raise TypeError, \
'Template.prepend: cmd must be a string'
if kind not in stepkinds:
raise ValueError, \
'Template.prepend: bad kind ' + `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('\$IN\b', cmd):
raise ValueError, \
'Template.prepend: missing $IN in cmd'
if kind[1] == 'f' and not re.search('\$OUT\b', cmd):
raise ValueError, \
'Template.prepend: missing $OUT in cmd'
self.steps.insert(0, (cmd, kind))
# t.open(file, rw) returns a pipe or file object open for
# reading or writing; the file is the other end of the pipeline
def open(self, file, rw):
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 ' + `rw`
# t.open_r(file) and t.open_w(file) implement
# t.open(file, 'r') and t.open(file, 'w') respectively
def open_r(self, file):
if 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 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 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':
temp = tempfile.mktemp()
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
# Reliably quote a string as a single argument for /bin/sh
_safechars = string.letters + string.digits + '!@%_-+=:,./' # Safe unquoted
_funnychars = '"`$\\' # Unsafe inside "double quotes"
def quote(file):
for c in file:
if c not in _safechars:
break
else:
return file
if '\'' not in file:
return '\'' + file + '\''
res = ''
for c in file:
if c in _funnychars:
c = '\\' + c
res = res + c
return '"' + res + '"'
# Small test program and example
def test():
print 'Testing...'
t = Template()
t.append('togif $IN $OUT', 'ff')
t.append('giftoppm', '--')
t.append('ppmtogif >$OUT', '-f')
t.append('fromgif $IN $OUT', 'ff')
t.debug(1)
FILE = '/usr/local/images/rgb/rogues/guido.rgb'
t.copy(FILE, '@temp')
print 'Done.'