pipes —- Interface to shell pipelines

源代码:Lib/pipes.py


The pipes module defines a class to abstract the concept of a pipeline—- a sequence of converters from one file to another.

Because the module uses /bin/sh command lines, a POSIX or compatibleshell for os.system() and os.popen() is required.

The pipes module defines the following class:

  • class pipes.Template
  • An abstraction of a pipeline.

示例:

  1. >>> import pipes
  2. >>> t = pipes.Template()
  3. >>> t.append('tr a-z A-Z', '--')
  4. >>> f = t.open('pipefile', 'w')
  5. >>> f.write('hello world')
  6. >>> f.close()
  7. >>> open('pipefile').read()
  8. 'HELLO WORLD'

Template Objects

Template objects following methods:

  • Template.reset()
  • Restore a pipeline template to its initial state.

  • Template.clone()

  • Return a new, equivalent, pipeline template.

  • Template.debug(flag)

  • If flag is true, turn debugging on. Otherwise, turn debugging off. Whendebugging is on, commands to be executed are printed, and the shell is givenset -x command to be more verbose.

  • Template.append(cmd, kind)

  • Append a new action at the end. The cmd variable must be a valid bourne shellcommand. The kind variable consists of two letters.

The first letter can be either of '-' (which means the command reads itsstandard input), 'f' (which means the commands reads a given file on thecommand line) or '.' (which means the commands reads no input, and hencemust be first.)

Similarly, the second letter can be either of '-' (which means the commandwrites to standard output), 'f' (which means the command writes a file onthe command line) or '.' (which means the command does not write anything,and hence must be last.)

  • Template.prepend(cmd, kind)
  • Add a new action at the beginning. See append() for explanations of thearguments.

  • Template.open(file, mode)

  • Return a file-like object, open to file, but read from or written to by thepipeline. Note that only one of 'r', 'w' may be given.

  • Template.copy(infile, outfile)

  • Copy infile to outfile through the pipe.