Generating PDF - "Unix Pipe Line" - Python Script for Beginners

# Author : mounicraju@gmail.com

import sys
import subprocess
from PDFWriter import PDFWriter

def error_exit(message):
    sys.stderr.write(message + '\n')
    sys.stderr.write("Terminating.\n")
    sys.exit(1)

def main():
    try:
        # creating and setting up a PDFWriter instance.
        pw = PDFWriter("PopenTo.pdf")
        pw.setFont("Courier", 12)
        pw.setHeader("Use subprocess.Popen for reading pipe and writing to PDF.")
        pw.setFooter("Done using selpg, xtopdf, Python and ReportLab, on Linux.")
        pipe = subprocess.Popen("nl -ba 1000-lines.txt | selpg -s3 -e5", \
        shell=True, bufsize=-1, stdout=subprocess.PIPE, 
        stderr=sys.stderr).stdout
        

        # Reading  from the pipeline and writing the data to PDF, using the PDFWriter instance.

        for idx, line in enumerate(pipe):

            pw.writeLine(str(idx).zfill(8) + ": " + line)
    except IOError as ioe:
        error_exit("Caught IOError: {}".format(str(ioe)))
    except Exception as e:
        error_exit("Caught Exception: {}".format(str(e)))
    finally:
        pw.close()
main()