Calculating the start time of a process

A quick script that calculate the start time of a process in Linux:

	#!/usr/bin/env python
	# vim: tabstop=4 expandtab shiftwidth=4 softtabstop=4 textwidth=79 autoindent
	"""
	Python source code
	Last modified: 12 Dec 2013 - 14:43
	Last author: Laban Mwangi
	Calculates the start of a process based on it's /proc/pid/stat file and
	the system uptime from /proc/uptime.
	Rough hewn - No exception handling
	Example:
	# echo python pid_start.py -p $$
	python pid_start.py -p 8153
	# python pid_start.py -p $$
	Process 8153 started 1:05:28.800000 ago
	Start time: 2013-12-12 13:56:39.081335
	"""
	import optparse
	import os
	import sys
	import datetime
	def calc_pid_start_time (args):
	pid = args.pid
	clock_ticks = os.sysconf("SC_CLK_TCK")
	start_time_after_boot = float(open("/proc/%d/stat" % pid).read().split()[21])
	seconds_since_boot = float(open("/proc/uptime").read().split()[0])
	start_time_seconds = seconds_since_boot - start_time_after_boot / clock_ticks
	start_time_delta = datetime.timedelta(seconds=start_time_seconds)
	print "Process %d started %s ago" % (pid, start_time_delta)
	print "Start time: ", datetime.datetime.now() - start_time_delta
	def main():
	"""Main function. Called when this file is a shell script"""
	usage = "usage: %prog [options]"
	parser = optparse.OptionParser(usage)
	parser.add_option("-p", "--pid", dest="pid",
	default="1", type="int",
	help="PID of process")
	(options, args) = parser.parse_args()
	calc_pid_start_time(options)
	if __name__ == '__main__':
	main()

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