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My first ever Python program, comments welcome

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  My first ever Python program, comments welcome Lipska the Kat <lipska@lipskathekat.com> - 2012-07-21 20:08 +0100
    Re: My first ever Python program, comments welcome Ian Foote <ian@feete.org> - 2012-07-21 20:34 +0100
    Re: My first ever Python program, comments welcome MRAB <python@mrabarnett.plus.com> - 2012-07-21 20:40 +0100
      Re: My first ever Python program, comments welcome Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-22 00:32 +0000
        Re: My first ever Python program, comments welcome MRAB <python@mrabarnett.plus.com> - 2012-07-22 02:56 +0100
        Re: My first ever Python program, comments welcome Chris Angelico <rosuav@gmail.com> - 2012-07-22 11:59 +1000
        Re: My first ever Python program, comments welcome Dave Angel <d@davea.name> - 2012-07-21 22:01 -0400
    Re: My first ever Python program, comments welcome Dave Angel <d@davea.name> - 2012-07-21 16:10 -0400
      Re: My first ever Python program, comments welcome Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-22 00:56 +0000
      Re: My first ever Python program, comments welcome rusi <rustompmody@gmail.com> - 2012-07-21 19:55 -0700
        Re: My first ever Python program, comments welcome Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-22 09:14 +0100
        Re: My first ever Python program, comments welcome Lipska the Kat <lipska@lipskathekat.com> - 2012-07-22 10:20 +0100
          Re: My first ever Python program, comments welcome rusi <rustompmody@gmail.com> - 2012-07-22 09:18 -0700
            Re: My first ever Python program, comments welcome Lipska the Kat <lipska@lipskathekat.com> - 2012-07-22 18:23 +0100
              Re: My first ever Python program, comments welcome rusi <rustompmody@gmail.com> - 2012-07-23 22:13 -0700
                Re: My first ever Python program, comments welcome Lipska the Kat <lipskathekat@yahoo.co.uk> - 2012-07-24 12:34 +0100
      Re: My first ever Python program, comments welcome Lipska the Kat <lipska@lipskathekat.com> - 2012-07-22 09:37 +0100
        Re: My first ever Python program, comments welcome Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-22 03:49 -0500
        Re: My first ever Python program, comments welcome Chris Angelico <rosuav@gmail.com> - 2012-07-22 20:17 +1000
          Re: My first ever Python program, comments welcome Lipska the Kat <lipska@lipskathekat.com> - 2012-07-22 13:36 +0100
        Re: My first ever Python program, comments welcome David <bouncingcats@gmail.com> - 2012-07-22 20:46 +1000
    Re: My first ever Python program, comments welcome Peter Otten <__peter__@web.de> - 2012-07-22 09:56 +0200
    Re: My first ever Python program, comments welcome "Ivan@work" <ivan.cvetkovic@pakel.hr> - 2012-07-23 09:12 +0200

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#25807

On 22/07/2012, Lipska the Kat <lipska@lipskathekat.com> wrote:
> On 21/07/12 21:10, Dave Angel wrote:
>>
>> A totally off-the-wall query.  Are you using a source control system,
>> such as git ?  It can make you much braver about refactoring a working
>> program.
>
> Thanks for your comments, I've taken them on board,
> I'm most familiar with with cvs and svn for source control. I've also
> used Microsoft source safe. I generally just use what's given to me by
> whoever is paying me and don't worry too much about the details. Many in
> the Linux world seem to use git. Seeing as I've been using Linux at home
> since the early days of slackware I suppose I'd better look into it.

What Dave said. I used CVS briefly and then git and its gui tools for
last 5 years.
Took me a while to get comfortable with it, but now it turns managing complex,
evolving text files into fun and I cannot imagine working without its power and
flexibility. First thing I do on any programming task: git init

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#25798

Lipska the Kat wrote:

> Greetings Pythoners
> 
> A short while back I posted a message that described a task I had set
> myself. I wanted to implement the following bash shell script in Python
> 
> Here's the script
> 
> sort -nr $1 | head -${2:-10}
> 
> this script takes a filename and an optional number of lines to display
> and sorts the lines in numerical order, printing them to standard out.
> if no optional number of lines are input the script prints 10 lines
> 
> Here's the file.
> 
> 50	Parrots
> 12	Storage Jars
> 6	Lemon Currys
> 2	Pythons
> 14	Spam Fritters
> 23	Flying Circuses
> 1	Meaning Of Life
> 123	Holy Grails
> 76	Secret Policemans Balls
> 8	Something Completely Differents
> 12	Lives of Brian
> 49	Spatulas
> 
> 
> ... and here's my very first attempt at a Python program
> I'd be interested to know what you think, you can't hurt my feelings
> just be brutal (but fair). There is very little error checking as you
> can see and I'm sure you can crash the program easily.
> 'Better' implementations most welcome

> #! /usr/bin/env python3.2
> 
> import fileinput
> from sys import argv
> from operator import itemgetter
> 
> l=[]
> t = tuple
> filename=argv[1]
> lineCount=10
> 
> with fileinput.input(files=(filename)) as f:

Note that (filename) is not a tuple, just a string surrounded by superfluous 
parens. 

>>> filename = "foo.bar"
>>> (filename)
'foo.bar'
>>> (filename,)
('foo.bar',)
>>> filename,
('foo.bar',)

You are lucky that FileInput() tests if its files argument is just a single 
string.

>         for line in f:
>                 t=(line.split('\t'))
>                 t[0]=int(t[0])
>                 l.append(t)
>         l=sorted(l, key=itemgetter(0))
> 
>         try:    
>                 inCount = int(argv[2])
>                 lineCount = inCount
>         except IndexError:
>                 #just catch the error and continue              
>                 None
> 
>         for c in range(lineCount):
>                 t=l[c]
>                 print(t[0], t[1], sep='\t', end='')
> 

I prefer a more structured approach even for such a tiny program:

- process all commandline args
- read data
- sort
- clip extra lines
- write data

I'd break it into these functions:

def get_commmandline_args():
    """Recommended library: argparse.
       Its FileType can deal with stdin/stdout.
    """
def get_quantity(line):
    return int(line.split("\t", 1)[0])

def sorted_by_quantity(lines):
    """Leaves the lines intact, so you don't 
       have to reassemble them later on."""
    return sorted(lines, key=get_quantity)

def head(lines, count):
    """Have a look at itertools.islice() for a more
       general approach"""
    return lines[:count]

if __name__ == "__main__":
    # protecting the script body allows you to import
    # the script as a library into other programs
    # and reuse its functions and classes.
    # Also: play nice with pydoc. Try
    # $ python -m pydoc -w ./yourscript.py

    args = get_commandline_args()
    with args.infile as f:
        lines = sorted_by_quantity(f)
    with args.outfile as f:
        f.writelines(head(lines, args.line_count))

Note that if you want to handle large files gracefully you need to recombine 
sorted_by_quantity() and head() (have a look at heapq.nsmallest() which was 
already mentioned in the other thread).

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#25842

On 21.07.2012 21:08, Lipska the Kat wrote:
> Greetings Pythoners
>
> A short while back I posted a message that described a task I had set
> myself. I wanted to implement the following bash shell script in Python
>
> Here's the script
>
> sort -nr $1 | head -${2:-10}
>
> this script takes a filename and an optional number of lines to display
> and sorts the lines in numerical order, printing them to standard out.
> if no optional number of lines are input the script prints 10 lines
>
> Here's the file.
>
> 50    Parrots
> 12    Storage Jars
> 6    Lemon Currys
> 2    Pythons
> 14    Spam Fritters
> 23    Flying Circuses
> 1    Meaning Of Life
> 123    Holy Grails
> 76    Secret Policemans Balls
> 8    Something Completely Differents
> 12    Lives of Brian
> 49    Spatulas
>
>
> ... and here's my very first attempt at a Python program
> I'd be interested to know what you think, you can't hurt my feelings
> just be brutal (but fair). There is very little error checking as you
> can see and I'm sure you can crash the program easily.
> 'Better' implementations most welcome
>
> #! /usr/bin/env python3.2
>
> import fileinput
> from sys import argv
> from operator import itemgetter
>
> l=[]

You can do without this, see below.

> t = tuple

This initialization does nothing. Assignment t=(line.split('\t')) makes 
`t` a list (not a tuple), discarding any previous value. And you don't 
really need t:

> with fileinput.input(files=(filename)) as f:
>      for line in f:
>          t=(line.split('\t'))
>          t[0]=int(t[0])
>          l.append(t)

List comprehension is your friend, and now you don't need to initialize 
l to an empty list.

with open(filename) as f:
     l = [line.split('\t') for line in f]

The first element of each row is now a string, but it's easy to fix:

>      l=sorted(l, key=itemgetter(0))

Use in-place sorting and cast the sorting element to int

l.sort(key=lambda t: int(t[0]))


>          inCount = int(argv[2])
>          lineCount = inCount

lineCount = int(argv[2]) works just fine


>
>      for c in range(lineCount):
>          t=l[c]
>          print(t[0], t[1], sep='\t', end='')

Whenever you write "for i in range(n)" you're (probably) doing it wrong. 
Here you can use list slicing, and as a bonus the program doesn't bomb 
when lineCount is greater than length(l)

for t in l[:lineCount]:
     print(t[0], t[1], sep='\t', end='')

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