import sys
def run_pipeline_to_read_output(pipeline,**kwargs):
    """Function to run a command pipeline and return file to read its output as bytes."""
    if not('stdin' in kwargs and kwargs['stdin']): # if no alternate specified...
        kwargs['stdin']=sys.stdin # ...first command gets stdin
    kwargs['stdout']=PIPE # all stdout goes to a pipe
    for cmd in pipeline: # each command...
        kwargs['stdin']=Popen(cmd,**kwargs).stdout # ...is started with output to next stdin
    return kwargs['stdin'] # return read end of last pipe for caller to read bytes from

if __name__=='__main__':
    pipeline=[]
    pipeline.append(['ls','-l'])
    pipeline.append(['egrep',r'\.py$'])
    pipeline.append(['tail'])
    file=run_pipeline_to_read_output(pipeline)
    for line in file:
        print(repr(line))
    file.close()