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:

>>> import pipes
>>> t = pipes.Template()
>>> t.append('tr a-z A-Z', '--')
>>> f = t.open('pipefile', 'w')
>>> f.write('hello world')
>>> f.close()
>>> open('pipefile').read()
'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.