[Tutor] Read from large text file, parse, find string, print string + line number to second text file.

Scurvy Scott etanes.rm at gmail.com
Sat Feb 2 05:57:41 CET 2013

And just for the records sake, this is what I've gotten and you guys
should see obviously that you helped a lot and I learned a thing or
two so I won't have to ask the same silly questions next time:

def main(mystring, infile, outfile):
    with open('infile', 'r') as inF:
		for index, line in enumerate(inF):
			if myString in line:
				newfile.write("string %s found on line #%d" (line, index))
print "complete."

if __name__ == '__main__':
   import sys
   newfile = open('outfile', 'w')
   help_text = "usage: python scanfile.py STRINGTOSEARCH
   if '-h' in sys.argv or '--help' in sys.argv or len(sys.argv) == 0:
	   print (help_text)
   myString = sys.argv[1]
   infile = sys.argv[2]
   outfile = sys.argv[3]
   main(mystring, infile, outfile)

Look right to you? Looks okay to me, except maybe the three ORs in the
information line, is there a more pythonic way to accomplish that


On Fri, Feb 1, 2013 at 8:31 PM, Scurvy Scott <etanes.rm at gmail.com> wrote:
>> Best practice is to check if your program is being run as a script before
>> doing anything. That way you can still import the module for testing or
>> similar:
>> def main(mystring, infile, outfile):
>>    # do stuff here
>> if __name__ == '__main__':
>>    # Running as a script.
>>    import sys
>>    mystring = sys.argv[1]
>>    infile = sys.argv[2]
>>    outfile = sys.argv[3]
>>    main(mystring, infile, outfile)
>> Best practice for scripts (not just Python scripts, but *any* script) is to
>> provide help when asked. Insert this after the "import sys" line, before you
>> start processing:
>>    if '-h' in sys.argv or '--help' in sys.argv:
>>        print(help_text)
>>        sys.exit()
>> If your argument processing is more complicated that above, you should use
>> one of the three argument parsing modules that Python provides:
>> http://docs.python.org/2/library/getopt.html
>> http://docs.python.org/2/library/optparse.html (deprecated -- do not use
>> this for new code)
>> http://docs.python.org/2/library/argparse.html
>> getopt is (in my opinion) the simplest to get started, but the weakest.
>> There are also third-party argument parsers that you could use. Here's one
>> which I have never used but am intrigued by:
>> http://docopt.org/
>> --
>> Steven
>> _______________________________________________
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> Steve-
>  thanks a lot for showing me the if __name__ = main part
> I've often wondered how it was used and it didn't make sense until I
> saw it in my own code if that makes any sense.
> Also appreciate the help on the "instructional" side of things.
> One question related to the instruction aspect- does this make sense to you?
> If len(sys.argv) == 0:
>     print "usage: etc etc etc"
> Nick, Dave, and Steve, again, you guys are awesome. Thanks for all your help.
> Scott

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